sailboat black water tank

Yachting Monthly

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What you need to know about a yacht’s black water waste tank

• Toby Heppell
• March 24, 2023

It is now mandatory in most countries to make provision for sewage to be pumped ashore rather than disposed of at sea. So it may be time to install a black water waste holding tank, writes Duncan Kent

Prior to the new millennium, little thought was given to waste disposal from a vessel. Anything you didn’t want on board invariably went straight over the side, including human waste. Thankfully, these days it’s a different matter altogether. Rubbish is widely recycled worldwide, so keeping it on board until going ashore is commonplace, even when ocean sailing. However, black water (sewage) disposal is not such a simple problem to solve, especially on smaller vessels, and it’s of particular concern when you are coastal cruising, anchoring or mooring close to the shore.

Current waste tank regulations

Given the increasing popularity of many northern European, Mediterranean, Pacific and Caribbean anchorages today, I’m convinced no responsible yacht owner would be against banning the direct discharge of black water within at least three miles of the coast. Nothing spoils an early morning dip in crystal clear water more than coming across an unmentionable floating object!

At the time of writing, there are still no mandatory regulations concerning black water disposal at sea from privately owned leisure craft in UK waters, apart from the legal requirement to provide pump-out facilities on inland waterways, but the situation is rapidly changing as other countries update their rules.

Since 2006, the EU Recreational Craft Directive (RCD) has required all new vessels to ‘have provision for a holding tank to be fitted’, although that isn’t the same as actually having a holding tank fitted. Besides, this only applies to new vessels and simply requires a ‘diverter valve’ to be installed into the discharge pipe to enable the waste to be piped into a holding tank.

That said, each country has its own rules about this and some are far stricter than others. For instance, Norway has banned the discharge of sewage within 300m of its coastline, whereas Germany insists you’re 12 nautical miles away before you even think about it. And if you’re even spotted with bubbles emanating from your boat in a Turkish marina you could be fined massively and possibly even imprisoned!

Generally, a holding tank doesn’t necessarily have to be permanently installed (although thankfully most boatbuilders today do).

UK black water regulations currently only apply to inland waters

In theory you could simply divert the waste into a freestanding jerry can or similar for disposal ashore, but this could end up being very unpleasant in rough seas and awkward to empty ashore without considerable mess.

Many boatbuilders that do install them from new, however, often only do so for a single head, leaving others on larger, multi-head yachts to be effectively unusable in prohibited sea areas.

Waste tank system design

The most common setup in new production boats is to have all the waste go directly into the holding tank, which will have a pipe and deck fitting at the top for pumping out shoreside, like most inland waterways craft have. Seagoing vessels, however, will also have a large diameter outlet at the bottom of the tank, complete with a seacock to allow the waste to gravity-drain overboard when outside the local limit.

This isn’t always the easiest to provide if retrofitting a system, though, as hull and deck fittings ideally need to be aligned (for rodding if necessary) and clear of any other fittings. For this reason, some boat owners simply incorporate a diverter valve into the existing outlet hose from the toilet, allowing the waste to either be pumped directly into the sea or alternatively into a remotely positioned holding tank.

Quick switch: send waste overboard or into a tank with a diverter valve

If this tank only has a deck plate, when the tank is full you are compelled to find a pump-out station, rather than simply sail offshore to empty it.

Tank size: The size of the holding tank will usually be a compromise between the ideal capacity and the space available in a convenient locker.

It should be at least 20 litres capacity, but ideally you should allow for around five litres per person/per day for two days. This means a cruiser, regularly used by a couple plus two guests, should work on a minimum capacity of around 40 litres. Too small and you’ll need to empty it too often; too large and it will add considerable extra weight and use up valuable space.

Location: Most choose to utilise an under-bunk stowage bin as the location for a remote tank, although some boats might have enough room inside the heads. Ideally, it should be positioned as close to the toilet as possible in order to keep hose runs short, but not so close as to force tight bends into any of the pipework. Bear in mind that the longer the inlet hose, the more water you will need to pump down it to clear the waste.

Thought must also be given as to the accessibility of any pumps or diverter valves incorporated into the system and the ease with which all areas can be reached for seasonal cleaning or the clearance of the almost inevitable blockage.

A typical holding tank installation

There are numerous companies producing tanks capable of storing black water. These tanks can be manufactured from stainless steel, GRP or plastic, the latter being either flexible or rigid. Steel tanks are excellent in many respects, but sooner or later their welded seams will begin to rust, expedited by the corrosiveness of the waste. GRP is lighter than steel and almost as odour-free, provided the moulding is perfectly executed and there is no trace of porosity. By far the easiest material, especially for smaller craft, is thick-walled plastic.

Retailers sell a bewildering range of plastic tanks, even some multi-purpose tanks supposedly fit for fuel, water or waste. The truth is many aren’t up to the job so care must be taken when selecting one to make sure it’s suitable for black water.

Dometic’s 15 HTS polyethylene holding tank has 6.3mm walls and costs around £600

It is often difficult to spot the difference between a polyethylene (PE) tank (for fuel, fresh and grey water) and a polypropylene (for black water), but the latter is more resistant to corrosion and odour permeation. Wall thickness also needs to be at least 6mm (1/4in), preferably 8mm (3/8in).

A flexible tank can sometimes solve a tight space problem, but in order to avoid the bladder chafing through on a sharp edge, a smooth-sided box must first be built from plywood and GRP. This creates work and limits overall capacity, so in most cases a rigid tank will prove easier to install.

Choosing a standard tank, many of which are available off the shelf in odd shapes and sizes to fit bow and bilge lockers, will save you money over having a custom tank manufactured to your own specifications.

Modern yachts use gravity tanks to discharge waste

Ancillary equipment – Pumps

Whether you decide to go electric or manual, a tank discharge pump must be man enough for the job. It’s no use using 38mm (1½in) pipes, connectors, and hull fittings if the pump only has 25mm (1in) inlet/outlet spigots. Most manufacturers produce a pump specifically designed for the purpose, usually a large-bore, high-capacity diaphragm device that can be operated manually or electrically, with an integral, non-return valve in its outlet.

It’s also possible to buy and fit 12V macerator pumps that grind up the waste while pumping it out. Their advantage is that a slightly smaller diameter outlet hose can often be used, and the chance of a blockage is reduced. They do, however, use more water than a manual pump, thereby filling the holding tank more quickly.

In modern boats, gravity is usually used to discharge the tank overboard. Although to avoid the danger of blockages with this method the tank outlet and skin fitting need to be large, usually 75-100mm (3-4in) in diameter, which is often not a practical option on a small boat.

New gauges can now indicate the exact level of waste in your holding tank

Ancillary equipment – Valves

Diverter valves are widely available from numerous marine plumbing equipment suppliers and are usually designed for bulkhead mounting. For systems that are pumping out with a head higher than 1m, installing a non-return valve into the exit hose will be essential to stop the contents back-feeding. Once again all valves need to be 38mm (1½in) diameter.

Ancillary equipment – Pipework

This is an important part of the installation, not just for safety reasons, but to ensure no nasty odours can pervade the living quarters. All hoses must be of non-permeable, sanitation grade, flexible PVC and the genuine article will normally be marked accordingly. It’s not particularly cheap, but it’s worth every penny.

As with any sea toilet installation, if the bowl or holding tank are below sea level at any time all pipework connected to a skin fitting must contain a swan-neck bend with an anti-syphon valve at the top. These are freely available in most chandlers for a range of hose diameters. All joints must be double-clipped using good quality, stainless-steel hose clips.

A remote pumped waste tank helps if the layout is awkward

Level gauges: Both electrical and mechanical indicators are available for waste tanks, which differ slightly from the usual water tank sensor in that the sensors are encased to prevent solids from fouling the mechanism.

Gauges are available that indicate the exact level of waste in the tank, but for most installations a simple warning light when the tank is nearly full is adequate.

Ventilation and odour prevention

Venting the tank: The typical odours experienced with poorly installed holding tanks are usually caused by anaerobic bacteria forming in an oxygen-starved environment.

The key to preventing these smells emanating from the tank is ventilation. Supplying oxygen to the tank allows the aerobic bacteria, found naturally in human waste, to carry out the job of breaking itself down. Any gases produced in this process will then be dispersed into the outside air via an overboard vent, preferably installed away from the cockpit area.

Installing a holding tank can be tricky on smaller yachts

Commercially produced tanks are usually supplied with pre-formed inlets and outlets. One of these, positioned as high on the tank as possible, should be the ventilation pipe connection. The vent should ideally exit the tank vertically to prevent any solids blocking the pipe and should then continue to deck level or onto a shell-type skin fitting high on the topsides. The pipe run needs to be kept as short as possible and there should be no tight bends or kinks restricting the airflow. An odour-reducing, active carbon filter can also be installed into the vent pipe without restricting the airflow to the tank.

Water treatment

Water treatment devices, such as the Seasmart sanitation reservoir, are available to kill bacteria in the seawater as it is drawn into the toilet.

The device is plumbed into the inlet hose and contains an environmentally friendly sanitation fluid which, as well as combating incoming seawater bacteria and odour, also claims to reduce the build-up of limescale without having a detrimental effect on the natural aerobic bacteria in the tank.

Simple additives are also available that should eliminate odour from holding tanks and also encourage the breakdown of the waste by natural bacteria. But, whichever additive you choose, don’t be tempted to use domestic toilet cleaner or bleach in either the toilet or the waste holding tank.

US national symbol directing boaters to the nearest pump out station

International black water regulations

Although the UK hasn’t, as yet, implemented any regulations regarding black water waste or holding tanks for recreational craft beyond its inland waterways, the situation internationally is now developing fairly rapidly, and unevenly, with some countries taking a much stricter stance than others.

• France – Boats built after 1 January 2008, either French or foreign flagged, must be fitted with a treatment system or retention tank for black water if they want to access French rivers, ports, moorings or anchorages. Users of older vessels not equipped with treatment systems or holding tanks for black water must comply with the rules that prohibit black water discharge in ports and designated anchoring spots, and therefore use shoreside toilets. It’s forbidden to flush black water into canals and rivers.
• Netherlands – It’s prohibited to discharge black water from any pleasure boat in any inland waterway, lake, or territorial waters.
• Denmark – Boats built before 1 January 1980 do not need a holding tank and can discharge sewage two miles from shore. Boats built after 1 January 1980 but before 1 January 2000, less than 10.5m LOA or with a maximum beam of less than 2.8m, do not need to have a holding tank and can discharge sewage two miles from the shore. All boats built after 1 January 2000 must have a holding tank that can be emptied through a deck fitting.
• Finland – The discharge of untreated sewage from recreational craft is prohibited less than 12 miles from shore.
• Sweden – The discharge of black water and sewage into lakes, inland waters and territorial waters less then 12 miles from shore is strictly prohibited, with spot fines applicable.
• Spain – Vessels cannot discharge untreated sewage within 12 miles from shore.
• Greece – While not actually a legal requirement in Greece, regulations make having a holding tank a practical requirement. Caution should also be exerted when disposing of grey water.
• Turkey – The discharge of any kind of waste may be considered illegal.
• Norway – Discharge from toilets or holding tanks closer than 300m from shore is strictly prohibited.
• Belgium – It is prohibited to discharge or dump any solid or liquid materials which may pollute the water both inland and at sea.
• USA – Federal law states that untreated sewage cannot be discharged, from either a toilet or a holding tank, in inland waters or coastal waters less than three miles from shore.

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Marine Holding-Tank Sensors: How do you Know When the Black Water Level is at Red Alert?

External tank gauges take the guesswork out of liquid levels..

Knowing how full your holding tank is can mean more than simply having peace-of-mind. Whether you’re starting out on a Sunday daysail or a two-week inland cruise, one of your checklist items should always be “Check the tanks.” Unless you are far offshore, realizing the holding tank is full as you attempt to pump the head—or when you pick up the telltale odor from the overflow vent—can be a real problem.

Federal law mandates that all boats with permanent toilets have either an on-board treatment system or a holding tank to store wastewater. Many states with inland lakes and coastal areas have designated them as No Discharge Zones (NDZ) and require that the through-hull and Y-valve for direct discharge ports be sealed to prevent any discharge into the water.

From the freshwater supply to fuel and wastewater, knowing the level of all tanks is a must for comfortable and safe sailing. Several tank-monitor manufacturers now refer to three types of tanks: “fresh” for drinkable water, “gray” for drain water from sinks and showers, and “black” for wastewater holding tanks from toilets. State and federal regulations are changing to address these differences, but not all boats are plumbed with multiple tanks hooked to different through-hulls.

Most older and smaller boats do not have level gauges on any tanks. A good captain “just knew” about how full his tanks were or could judge the level by simply thumping the tank with his knuckles. Occasionally, if the tanks had inspection ports, a visual check with a flashlight or inserting a dipstick was sufficient.

Today, there are several options for measuring tank levels, starting with the simple internal float gauge and progressing to sophisticated ultrasonic capacitance or sonar internal probes. There also are various sensors designed to be mounted on the tank’s exterior, and those are our focus here. We’ll address sensors that are mounted internally in a future article.

What We Tested

Packaged kits containing externally mounted tank level sensors with remote reading displays are becoming increasingly popular due to the fact they don’t come into contact with the holding tank contents. Probes located inside the tank are more likely to be fouled, corrode, and need cleaning.

External sensors use basic capacitance sensors or the electronic Mirus detector cells that read liquid levels on the other side of plastic, polyethylene, and fiberglass tanks. External tank readers are for wastewater and fresh “sweet” water tanks, not aluminum or metal fuel tanks for diesel or gasoline. All of those we tested should work on standard tanks up to 3/8-inch thick, and all come with a one-year warranty.

When choosing a tank-level indicator, bear in mind that at least one side of the tank must be accessible for mounting the external sensor devices.

For this evaluation, Practical Sailor tested five external sensors with their mated display: Raritan Tank Monitor (1510012), Scad Profile Tank Monitor, SensaTank Marine 100, Snake River Acu-Gage Smart Mini, and Snake River Acu-Gage Three-Tank.

Raritan Tank Monitor

Raritan’s tank sensor works on 12-volt DC (other voltages are available). While it can display the liquid levels of four tanks, the kit comes with only two capacitance tank sensor modules. The kit also includes 10 feet of aluminum foil, a 3-amp fuse holder, 12 crimp splice connectors, and a display panel with screws and stick-on labels. These stickers—with universal symbols for “waste,” “gray,” and “fresh”—can be affixed to the display to identify the four buttons. PS testers questioned the durability of these stick-on labels.

The display panel is fairly small, measuring 2.25 inches high by 4.5 inches wide. It has four touch buttons for tank selection, and each has a corresponding hole for calibration. Five LED lights indicate the tank level: empty, quarter-full, half-full, three-quarters full, and full. Testers found these indicator lights to be dim and hard to see in daylight.

Raritan’s instructions are clear and well written—as long as you have a standard size tank. Tanks less than 7.5 inches tall or more than 20 inches tall require adjusting the amount of aluminum foil that is mounted to the side of the tanks.

Calibrating the Raritan is a simple a matter: fill a tank with water up to where you consider it full, then insert a small flat-head screwdriver into the hole above the selected tank’s touchbutton on the display panel, then turn it until all lights are on and then just the full light comes on. Repeat for each tank. The kit includes four small plastic plugs to insert in the holes once calibration is complete.

Before presstime, West Marine marked the Raritan’s Tank Monitor as a “clearance” item, discounting it to $224. Raritan plans this spring to release a new monitor, so stay tuned for its review in an update to this test.

Bottom Line: The Raritan unit provides standard tank monitor features with external capacitance sensors. We found its tech support and website to be lacking.

The Scad Solo Profile Series (TM01) holding-tank monitoring kit includes a very small 2-inch-by-3.5-inch display panel, five feet of aluminum sensor foil, and one capacitance external tank sensor module. The display panel has a membrane-covered mechanical switch labeled “Read,” five prominent LED lights (that illuminate quite brightly) above each of which are labeled tank status levels (from empty to full) and a “Tank Full” red LED. It also has two tiny buttons (marked “F” and “E”) for calibrating functions.

Installation of the Scad Solo got off to a rough start due to its lengthy and unclear instruction manuals: a six-page booklet for the external non-contact fluid level sensor and a 10-page manual for the display panel. That seemed like a lot of reading for what should be a simple installation and hook-up. Upon digesting the instructions, testers found the manuals to be extremely wordy and not explicit enough. In fact, we had to call the manufacturer twice for clarification. Scad immediately e-mailed a new version of the instructions and offered verbal help.

Part of the confusion stems from the fact that Scad offers several versions of the display, and it can be programmed to work with many different types of tank sensor devices. The model we tested is intended for a holding tank. Scad also offers sensors specifically for water tanks as well as display panels that monitor up to eight tanks (Profile TM02).

In response to PS testers’ difficulty in translating the instructions, Scad said it is now overhauling the manual to make it shorter and more concise.

What the instructions lacked, the company makes up for in customer service. Technical support is available via phone seven days a week, 365 days a year.

Our initial problems aside, the installation and testing went smoothly. The Scad Solo Profile monitoring panel and external sensor have some unique and interesting features, including the ability to be calibrated for more accurate readings when using oddly shaped tanks that may be custom fitted. It also has the ability to program the characteristics of different types of tank sensors such as several internally mounted devices and the standard float sensors. Third, it allows you to program and set exactly where you want both the “empty” and “full” levels to be on your tank. Fourth, the external tank sensor module has a green LED indicator light that glows when the panel’s “Read” button is pushed, to indicate that all wiring is working. Finally, the Solo designed for holding tanks has a large red LED light on the panel, marked “Tank Full,” that will illuminate when the tank is 85 percent full. It reads the tank level every half-hour, so there may be about a 30-minute delay before the alarm goes off.

The Scad Solo will monitor only one tank, and the kit comes with one sensor and one display panel. To monitor two tanks, Scad suggests installing a rotary switch at the display panel, wiring it to sensors on the tanks and simply switching from one tank to the other as needed.

Bottom Line: Our favorite in the single-tank category, the Scad Solo kit was the most accurate, has more programming and calibrating flexibility, and will handle irregular-shaped tanks. We also like the tech support availability.

SensaTank Marine 100

The SensaTank Marine 100, made by TouchSensor Technologies and distributed by West Marine, says “Holding Tank Monitor” on the box but will work on freshwater tanks as well. This kit can monitor three tanks and contains three sets of fluid-level external tank sensors.

Each set has four proprietary stick-on “Mirus” field-effect detector cell sensors—one each for full, quarter-, half-, and three-quarters full—all pre-wired to a plug. This plug connects to the interface board presumably located near the tanks. The kit includes 20 feet of CAT-5 type cable and connectors to wire to the remote display panel. The 3.5-by-5.5-inch panel comes with screws and a plug for mounting and connection to 12-volt DC. The kit included an AMP male plug but did not include a female plug, and instructions suggested cutting off the plug to wire up to power. The panel has three field-effect touch-sensor buttons identifying “Tank 1,” “Tank 2,” and “Tank 3,” and an LED lighted bar graph that illuminates progressively to show the level of the selected tank when the corresponding button is pushed.

It comes with a very simple two-page instruction sheet with good diagrams. The installation is fast and straightforward with “plug-and-play” wiring that is obvious and intuitive with little chance of mistakes. No calibration is required. However, it would help if the detector cell sensors were marked: “full, ¾, ½, ¼.” (There is no “empty” sensor.) We accidentally stuck the quarter-full sensor near the bottom and the full sensor too close to the top. Once affixed, the sensors are very difficult to move.

Operating the monitor is very simple, and reading the level status is straightforward. Pressing and holding the button for the desired tank will illuminate LEDs behind cutouts that clearly show the liquid level. The SensaTank also has a visual alarm: If the tank liquid level reaches either below the quarter-full sensor or up to the full sensor, the indicator light flashes two times per second.

Bottom Line: SensaTank Marine 100, our top choice for the multi-tank monitor kits, comes with all necessary wire, connectors, and equipment, is easy to install, and simple to operate. The LED indicator lights are bright with easy-to-read labels, and the empty and full lights will flash when in alarm condition.

Acu-Gage Smart Mini

Another single tank monitoring kit, the Acu-Gage Smart Mini, manufactured by Snake River Electronics (now owned by Diamond Distribution), looks and functions almost identical to the Scad Solo.

The kit comes with a small display panel with stick-on ID stickers (“Fresh,” “Grey,” “Black,” “Waste,” and “Diesel”) for the single panel button, a holder for fuses and crimp connectors, a Moda capacitance sensor module, and five feet of aluminum sensor tape. The display panel includes five LEDs marked “Empty” through “Full,” tiny calibrating buttons, and a larger tank reading button. The 10-page instruction booklet was straightforward and well written—although like the Scad, it too had an incomplete wiring diagram.

While the Acu-Gage and Scad Solo look similar, their electronics and software are different. The Acu-Gage does not have an LED on the sensors, a “Tank Full” alarm/LED, or the ability to program different types of sensor or calibrate for odd-shaped tanks. The Acu-Gage monitors one tank.

Bottom Line: The Smart Mini is a no-frills kit that works well and is the least expensive, but it lacks extra features, and current availability through local marine distributors is lacking.

Acu-Gage three tank

We also tested Snake River’s three-tank monitoring kit. It has a larger monitor panel than the Smart Mini, but it calibrates and operates the same. It also has two additional tank push buttons.

Testers noted that accuracy was a bit off during testing, but Snake River suggested that adjusting the tape application slightly will alleviate this.

Bottom Line: This Snake River unit functioned without any problems, and it’s reasonably priced. We would like to see Snake River improve its tech support and presence in the marine retail market.

The quality and workmanship of all the display panels we tested appear to be good or better. The products are small enough to mount just about anywhere, and all draw minimal amperage.

The cost per tank monitored is difficult to determine since we tested both single- and multi-tank sensors. If you need to monitor two or more tanks, a multi-tank display makes sense and may even save you time and money. Each manufacturer represented offers additional tank sensors, and some offer other displays that allow for more tanks to be monitored.

Rating the sensors’ accuracy also was difficult, since each of the capacitance foil sensors read the tank water levels a little differently. When the tank was half full (visually measured), only one lit up half, while one showed one-quarter, and the others three-quarters full.

That being said, we decided against choosing a Best Choice and Budget Buy, and instead recommend the two standouts in this test: the Scad Solo single-tank monitor and the SensaTank 100 multi-tank monitor.

The feature-laden Scad was a top performer in accuracy with its main drawback being the instructions that are being revised, and the SensaTank was easy to install, accurate, and had good tech support.

• How We Tested
• Practical Sailor Value Guide: External Holding Tank Sensors

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Boat Holding and Waste Tanks

Whether on the water in your boat or on the road in your motorhome, quality holding tanks and holding tank systems are essential to your plumbing system. Polyethylene tanks are sturdy, keeping wastewater (black water and gray water) where it belongs: out of sight (and smell). Check out Great Lakes Skipper's amazing discount prices on marine waste tanks and holding tanks, hoses, holding tank monitors, and more wastewater tanks, holding tank components and accessories by Bayliner, Raritan, MPI, Dometic, and more top brands.

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Deep Water Happy

Emptying your boat’s holding tank // black water tank.

• On January 20, 2022
• By Kimberly

There are two methods of emptying your holding tank; one is to travel at least three miles offshore and empty there, and the other is to come to a fuel dock that has a waste pump out, and empty the MSD – Marine Sanitation Device – there.

Pump Out Station

If you are pumping out at a pump out station, these are modern times! There is no more having to put huge amounts of downward pressure on the exit tube, or much risk of the tube popping out.

Most facilities now have serval standardized caps that screw into the boat and are the correct size! This is wonderful! This is brilliant!

First, locate your waste cap. Make sure not to mix it up with fuel or water. These three fluids should not mingle.

When you’re sure you have the correct, remove it. There will not be a chain holding it to the deck plate, probably, because it is necessary to completely remove it in order for the exit line tube to be inserted.

The attendant is going to take care of just about everything. They will insert the nozzle, start up the pump, and run the machinery.

There is not a gauge on exiting fluids, like on a fuel fill up, so you won’t really know how many gallons you are just to sending. There is a sight window, however, so you can see what’s leaving the boat.

It’s quite acceptable to look at your holding tank gauge, if you have one, and give the attendant and idea like, “halfway there,” Or “3/4 of the way to empty.”

There probably are no funny jokes that you can tell at this time, as the attendant will have heard everyone of them at least 50 times each.

When it seems that the tank is empty, you might opt to pump more water through the toilet, and empty that as well, sort of “flushing it out.”

The attendant will remove the nozzle, they might possibly suck up a bit of sea water to flush out their own line, and their job is done.

A gratuity for performing this valuable service for you would be appreciated by the dock hands, especially if they helped you get to the dock.

Pumping Out Offshore

1. gravity fed system.

We’ve only had one gravity tank in our fleet, and it was a pretty simple process of opening up valve, listening for “things “to fall out of the boat, and then closing the valve.

2. Electric Macerator System

For a more traditional macerator set up, you will need to open the macerator line’s thru hull fitting in the bilge or in a lazarette so the fluids can exit the boat.

On your electrical panel, there could possibly be as many as two buttons. One that is able to switch on and off, which supplies power to the pump.

Then a second switch, much like the bilge pump switch, that must be held in position, and once released, springs back to not running.

Think of this like a drill with a cord. It is plugged in, but not running. It requires your finger on the trigger to run, and when you let go, it quits running.

Power to the Pump

You’re going to turn on power to the pump, and then hold down the macerator button. The end of the button might turn red, indicating that it is performing its function, and you should hear a pump running noise.

How Will I Know…

In sailing class, everyone wants to know how will we know that the tank is empty. There are two methods.

One is for someone to position them self topsides, near the release valve, and watch. They will notice a lot of brown material in the water, then slightly more clear muddy material, then clean water flushing if you are running some water through the toilet to flush things out again.

As you rock and sail over waves, more material will flow out of the boat.

If that’s not possible, then listen. The macerator pump will sound like making a frozen drink, only not so violent.

First you will have more “rocky” type of noise, sort of like making a frozen drink and first grinding up the ice. Then, when the tank is closer to empty, the motor will free wheel and spin, like a frozen drink nearly completely blended.

3. Hand Pump Out System

If you are using the third system, a hand pump, you still must open the holding tank thru hall valve.

Go to where the pump is, and pump and pump pump until things run clear. It might take a bit of priming at the beginning to get the process started.

Close the Thru-Hull

Whether you are using an electric exit pump, or a manual exit pump, when finished; absolutely definitely make sure that you close the thru hull valve.

The action of you sailing along can allow backflow to enter the toilet, boil over the lip, onto the head sole, into the shower – you get the idea. ​

Close the macerator thru-hull fitting when finished, and de-power the pump on the electrical panel.

What to read next: 5 Things to Check Before Backing Your Boat Out of a Slip

Into the Water

Don’t forget that everything that touches your body can end up in the water.

Shampoo, conditioner, deodorant, toothpaste – everything gets into the water. Be sure your choices are biodegradable.

For extra-eco-conscious choices; select products that have biodegradable containers, and made from recycled materials – trips good!

If you are looking for ecoconscious choices, Stream2Sea   offers water-, reef-, and human-safe products tested to be safe for the environment.

I Don’t Go Anywhere Without :

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• Thank you Bill for being the Best Sailing Partner EVER!

About Kimberly

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THE PRUDENT MARINER // SAFETY AT SEAS SERIES INTRODUCTION // Deep Water Happy

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How To Pump Out Your Holding Tank

Last Updated by

Capt Chris German

June 15, 2022

Everyone Poops. One of the grossest mysteries of owning a boat is what happens when it goes down. Where does it go? How long does it stay? And how do I get rid of it?

The subject of holding tanks and poop is one that is almost too difficult to broach in polite company. No one wants to admit they even do it, let alone what they do with it afterwards. So today, we pull back the curtain and look deep into the subject that is pooping on a boat.

Table of contents

The black water tank

I am not sure that it Is it any coincidence that the most well known private mercenary force responsible for countless war crimes shares the same name as the tank that holds the foulest of human byproducts.

Black Water.

The very term brings up secrets, unmentionables and private human functions. So I guess it makes sense that they share a name.

The black water tank on a boat usually has a nasty smell and as such is usually located under the least desirable bunk on the boat- usually under the vee berth.  It gets this smell not from your colon necessarily, but from the sodden, festering marinated combination of all forms of human effluence. This mixed with paper products, water and stirred exuberantly by the motion of the boat and left in an oxygen free environment for partial anaerobic consumption is to blame.

It is these anaerobic bacteria, combined with the bacteria of your lower bowel that create a truly odoriferous experience for anyone forced to sleep in the vee berth or tasked with the duty of emptying said tank.

The grey water tank

This is the tank that holds the washing water on a boat. The grey water tank  is a much less innocuous sounding facility and not all boats have them.  Some boats combine grey and black water into one tank, while others separate them. If your boat navigates exclusively in non-discharge zones along Coastal and Inland waters, you are required to collect all of the “grey”water.

 Grey Water by definition may contain no fecal matter. It may, however, contain bacterias and soap products that are noxious to the water environment and should not be discharged in bodies of water that do not intersperse readily with the world ocean environment.

The presence of these bacteria, (particularly if you are one who urinates in the shower) can make this water very smelly and almost equally gross as black water. Other things like food particles, dirty clothes and bath water also give this water a distinctly disgusting quality. As such, it  should never be dispersed on any human or animals consumed plants or food sources.  

The fresh water tank

This tank should never be confused with either of the previously mentioned tanks as this is water that can be consumed by humans and animals. It really bears no relation to pumping out the holding tanks other than while you are at the pump out dock, oftentimes there is a fresh water hose available for potable water that should never be used in any way with your holding tanks.

You may also find the fresh water fill on the deck of your boat in a similar configuration to your waste water and holding tanks. Please never confuse these two filling ports on your boat and if you do decide to fill your freshwater tank while on the pump out dock, be sure to use the spigot that says potable or drinking water and never cross-contaminate the hose.

How to use the pump out dock

In many places around the world, a dock that is designed exclusively for pumping boats out is available to recreational boaters.  You will know it is a pump out dock because it should have lots of signs on it. It will have a prominent fixture on it that has a two inch flexible hose coming off the side. It is  likely to have a yellow or black handled ball valve at its end with a sight glass on it.

Not every pump out dock is the same and sometimes you are charged a fee to use the pump out, but the best communities I have found have free pump out services for the public. In the places I have lived where I used the pump out, namely Connecticut, North Carolina and Utah, the systems are pretty universal.

When you pull up to the pump out, you will likely encounter other boaters. Be considerate. If you have a 24 foot boat, please don’t use slips where a 65 foot boat can only park. Also,  please don't park right in the middle of a dock if it can fit more than one vessel.

Pull your boat to the end, but not so far that the hose will not reach your boat. Use your best judgement, but please be considerate to others.

Once you're docked, now is time to pump. Take the hose off the pumpout housing and drag it to your boat. You should have a pump out fitting that screws into your waste hole on your boat. They come in 2 inch and inch and half  threaded sizes so make sure you have the right size for your boat. Unscrew the deck cap and put the cap in a safe place so you don't drop it overboard.

Now, screw the pump out fitting into your waste hole tight enough so that air cannot escape but not so tight that you can’t ever get it out. Next, take the ball valve with sight glass and fit it onto the lip of your pump out fitting. There should be two levers on either side of the valve that flip upward to secure the hose fitting to your pump out fitting. Once you have flipped those levers, you can turn the pump out on by pressing the green button on the pump out housing.

You will now hear a pump kick on and you can open the handle on the ball valve. You should see a brown or grey slurry get sucked up into the hose. Sometimes you may need to open and close the handle partially to establish the suction on weaker pumps.

The hose will then transport the fluids up to the housing and then pump it down the docks to a septic tank or sewer system on shore.

You will know you're finished when the pump out can no longer pull a steady stream of fluid from your tank by looking in the sight glass. Close the valve and unlatch the levers and pull the hose off of your pump out fitting. Place it in the water while you take the cap off your grey water tank and repeat the process.

When you have pumped both tanks dry, open the vale and place it back in the water. This will suck up sea water and flush any solids that got stuck in the line up into the system. Close the valve and neatly coil the hose back onto the hook on the pump out housing.

I like to use the hose that is designated for pump out to wash down the area and put a little fresh water into the tanks. You can repeat the pump out process if you want to get that rinse water out, but I find it dislodges solids over time so I like to leave a few inches of water in my tanks after I have pumped them out.

Now you can flush a sanitizing pouch, also known as a “blueberry”, into the tanks and be on your merry way.

The pump out boat

There is another service offered by some marinas and municipalities - a mobile pump out.  A pump out system is installed on a boat that can come directly to your boat on the dock or mooring. Sometimes this is a free service and other times it is pay service, but either way you should tip the pump out guy who drives the boat because it's a nasty job.

Many times the pump out guy will do all the work, but you really can help him by telling him if your boat is vented or not. Vented boats have a tube that vents out the side or through the cabin top that allows vapors to escape and prevents a vacuum from forming when you pump the tanks.

If your boat is not vented, you run the risk of imploding the tanks when you pump out, so you will need to open the traps in the toilet to allow air to come in while pumping out.  This goes for the pump out dock as well, but in my experience is much more important with the pump out boat because they generally have stronger pumps since they don't have to suck the fluids uphill to a facility.

Keeping you and your tank healthy

There are a few million infectious diseases in a holding  tank that can get all over the place when you are pumping out. Taking precautions like not touching your face, washing your hands, using hand sanitizer and using gloves should keep you safe. Some folks like to wear a face shield and apron when they use the pump out cause there is a chance that things can spray and get really nasty.

You can also minimize the colonization of bacteria in your holding tank by pumping it regularly and using additives that help break down the solids and decompose them into a more fluid consistency. One of our favorites is Happy Camper , an additive you mix with water and pour into your holding tank. It kills odors, breaks down solids and makes living with holding tanks that much more appealing.

Another thing you could do occasionally is wash out your holding tank with a multi-directional hose fitting. They are available online. We use a long rod to stir our tanks every once in a while in addition to the hose  to break clumps of paper products and chunkids.

There is also a theory that if you dump a couple bags of ice into your tank that the ice chucks will scour the solids from your tanks and help clean it out. I think this could work on a boat that is moored much better than one at the dock, but try and let me know how it works for you.

Finally, bleach will sanitize your tank but it also kills all the good microbes that help break down the materials in your tank. Once a season, I have been known to give my plastic tanks a good cleaning with bleach but I would never use bleach on a bladder or non-rigid tank for fear that it degrades the fabric.

Clogs will happen

It's a nightmare when it does happen, but clogs do occur. Usually it is because someone flushed something they shouldn’t have flushed and it gums up the tank or lines.

A key to preventing clogs, especially if you have young ladies on your vessel, is to make it clear to them that nothing goes in the toilet that hasn’t gone through your mouth first. Keeping a trash can nearby in the head helps enforce this rule. Some folks even resort to private shaming with a sign in their head that reminds their guests of this rule.

Whatever you do, keeping that stuff out of the tank is your first option. If it does get in there or you have a clog from some other way, there is not much to do to fix it but get manual. Don your face shield and gloves and go in to find where the clog is located and break it up.

Toilet paper is a big culprit when it comes to clogs so using fast decomposing paper is a good choice. Other ways it can happen is when your guests don’t use enough water to wash the solids down. If this is the case, you might be able to use a high pressure nozzle with your hose to blow the clog apart. Keep an eye on your sight glass to make sure you have washed the entire clog out of your tank and make sure you don't use that hose for any potable water purposes.

Pumping a boat out is a dirty business but we all have to do it. Taking care to keep your tank healthy and free of clogs will cut down on smells and make your vee berth that much better to sleep in. Don't be a jerk at the dock and if all else fails, ask your fellow boaters for a hand in learning how to pump your boat out. Most people are pretty nice when it comes to pumping out because no one likes to do it. Thanks for reading. Do good, have fun, and sail far.

Related Articles

Capt Chris German is a life long sailor and licensed captain who has taught thousands to sail over the last 20 years. In 2007, he founded a US Sailing-based community sailing school in Bridgeport, CT for inner city youth and families. When Hurricane Sandy forced him to abandon those efforts, he moved to North Carolina where he set out to share this love for broadcasting and sailing with a growing web-based television audience through The Charted Life Television Network.

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18 Gallon V-Shaped Boat Water/Holding Tank - WH-2018

Price: $272.00

18 Gallon V-Shaped Water & Holding Tank

Tank Dimensions 24.5″ L x 20″ W x 10″ H

These water tanks are suitable for the storage of potable water, freshwater, and wastewater (grey water, black water).

Trionic water and wastewater holding tanks are rotationally molded into durable, seamless, one-piece, non-corrosive tanks. Each tank fully complies with FDA regulation 21 CFR 177.1520 and meets all U.S. Coast Guard regulations. Each Water/Holding tank has (2) 1-1/2″ FPT and (2) 1/2″ FPT threaded openings. Openings on all tanks feature female National Pipe Threads (NPT) and are located on one end of the tank. Unused openings can be capped.

All tanks are 3/8″ average wall thickness.

V shape is ideal for fitting into the bow of some boats - Boat Bow Tank

Note: The bottom of tanks should be fully supported when installed and use a 12″ minimum length of flexible hose to hose barb fittings.

Custom fitting locations are available on orders of at least 5 tanks.

All Trionic Corp products offer a one-year warranty covering materials and workmanship. Warranty does not cover misuse or abuse of the products.

This same tank is also available as a blank tank without the threaded openings. These tanks allow the user to locate openings in the exact locations dictated by their installation requirements. Trionic Corp’s CF-60 Custom Fittings kit makes the installation of a blank tank quick and easy.

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The Boat Galley

making boat life better

What Size Holding Tank Should You Have on a Boat?

Published on January 17, 2015 ; last updated on January 24, 2023 by Carolyn Shearlock

I doubt that many of us really consider the size of the holding tank when buying a boat. Yet, if you’re going to spend more than a weekend at a time aboard, it can be pretty important unless you have a composting head.

• If your marina requires you to move the boat to a pumpout station, how often do you want to do that?
• Most marinas include one pumpout a week in their price — extras typically cost $5 to $10.
• If you’re at anchor, you’ll have to either go to a pumpout station or far enough offshore that you can dump the tank in deep water (here in the Florida Keys, the law is  12 miles offshore). A small holding tank will really limit your time in nice anchorages.

Yes, there are some countries that not only don’t require pumpouts, they don’t have pumpout facilities. Mexico, Central America and most of the Caribbean nations fall into this group. Most boats either discharge directly overboard or to the holding tank and then discharge overboard once out of an anchorage.

Anywhere else, you have to live with pumpout rules.

And so the question becomes what size holding tank do you need? Ours is 18 gallons and even with not putting paper in the toilet (it takes up space as well as makes the toilet more susceptible to clogs) and being judicious in how much water we use to flush, we can’t go a week between pump outs — we opt for twice a week pumpouts with two people aboard. We might be able to go five days between pumpouts at anchor, but feel more comfortable getting pumped out at four.

The problem of a too-small holding tank was just one of the factors that led us to switch to a composting head just a year after we bought this boat.

To help others who are looking at boats and comparing features, please leave a note with the size of your holding tank, number of people and how often you have to get pumped out if living aboard full time.

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Reader Interactions

Debra Bryan says

January 17, 2015 at 12:58 pm

We have a 30 gallon (and a 15, unused so far), with 2 people aboard full time. Longest we have gone between pump outs is 12 days; might have made another day or two, but pump out was available so why not 🙂

January 17, 2015 at 7:01 am

Our holding tank is 40 gal and we have two people on board. We are at anchor 99% of the time, and cruise all year in Mexico. No paper goes into the heads, and not much water. My husband tends to pee discreetly overboard, so that saves some room, lol. Having said all that, we can generally go about 3 weeks, maybe a bit longer before we have to go offshore outside the anchorages and pump out.

Rebecca Hammond Vaughan says

January 17, 2015 at 1:29 pm

2 heads @ 15 gallons each, 2 people, no paper, we can make it about a week.

Michael Mangione says

January 17, 2015 at 1:31 pm

2 people, 1 head, 35 gallons, no paper, no problem for a week to 10 days.

January 17, 2015 at 2:21 pm

I feel like I need to add about the fresh water flush. I used a T fitting off the lavatory sink drain, I connected the intake on the head to this T. Should we get into a situation where water conservation is much more important, we can open the intake seacock and flush with salt water. We wash our hands in the lavatory, and re-use that water when we need to flush. Its a fresh water flush, but we are using the water twice.

Arion McCartney says

January 17, 2015 at 10:23 am

Hi Michael, I think this is a good idea. Do you have a seperate holding tank for the gray water that comes from your lavatory sink? How much extra space does this take up, not to mention the extra plumbing.

Stephen Leach says

February 10, 2021 at 10:46 am

You What ????? You wash your hands in the lavatory !!!

July 14, 2021 at 4:16 am

I have a 100 gallon tank and if it goes more than 2 days between pump outs it means business was dead on a busy day have to pump out multiple times little to no water is used I have the intake seacock closed and provide a container of water for people to use if needed this makes a huge difference it’s 95% pee but it’s a party boat typically has 30-45 passengers onboard for 4 hour cruises I recommend getting the biggest tank possible especially if your harbor doesn’t have a pumpout boat who will pump you out underway the 20 minutes or so to go get pumped out multiple times a day is a major pain

Sean Rhody says

January 17, 2015 at 1:35 pm

Many of these say they put no paper in the toilet, what do they do with it?

The Boat Galley says

January 17, 2015 at 1:52 pm

Here’s my post on it: https://theboatgalley.com/clog-free-head/ — I’d say the majority of people living aboard do NOT flush paper but instead put it in a lidded trash can or bag.

Daniel Herrigstad says

September 23, 2020 at 1:07 pm

Hi Carolyn: I read your article above and the sign you have posted by the toilet. I see you have (had) a LaVac toilet. I just bought a Nauticat that has two of them. What is this “hole in the U-hose…” you’re supposed to put your finger over? These are interesting toilets the way they suck the lid down so firmly, but they seem to work ok, but I’m rebuilding the pumps with new kits that are on the way. Thx! Dan

Carolyn Shearlock says

September 23, 2020 at 1:30 pm

It’s the specific anti-siphon valve that was used in our boat’s installation and is not typical of LeVacs. That said, it’s a GREAT toilet.

Leigh Ann Bishop Long says

January 20, 2015 at 11:44 am

If it didn’t go in your mouth, don’t put it in my loo!

Dean Calkins says

January 17, 2015 at 1:36 pm

2 heads with a 28 gallon tank 2 people about 2 weeks is tops for us!

Kaptnuno says

January 17, 2015 at 7:39 am

I changed to a composting toilet. Tired of bad smells, clogs and noise of the waste in the septic. 🙂

Nuno Antunes says

January 17, 2015 at 1:40 pm

Looking forward for your thoughts in composting toilets! 🙂

Mary E Dixon says

January 17, 2015 at 1:51 pm

A key factor is using fresh water for flushing. We only use fresh water for flushing solids. Paper goes in a small trash can with tight fitting lid.

January 17, 2015 at 1:56 pm

I’m curious why using fresh water makes it so you can go longer before the tank is full? Do you use less?

Camille Rogers says

January 17, 2015 at 1:59 pm

2 – 20 gallons holding tanks. A week is really stretching it.

January 17, 2015 at 2:00 pm

We keep a gal jug of water in head area & pour nuf water to flush solids. We keep our head pump set on dry all the time.

Bill Dixon says

January 17, 2015 at 2:14 pm

It’s not the “fresh ” water, it’s the use of a jug instead of the head pump. We add less water to the waste stream.

January 17, 2015 at 2:43 pm

Okay, now I understand! Thanks Bill!

Ginni G says

January 17, 2015 at 8:07 am

We have a 20 gallon tank with a 9 gallon Sealand Traveller toilet. We have guests every week end. In addition, we sometimes stay by ourselves one or two days beyond that. We pump out every other week end.

Ted Reshetiloff says

January 17, 2015 at 2:09 pm

36 gallon trionic tank Family of 4. Full time live aboard. We can go 10-14 days between pumping out. We have a pair of vacuflush heads that use fresh water to flush.

Ed Robinson says

45 gallons, 2 people, no paper. Could last 3 weeks but the odor gets bad within 2 weeks.

January 17, 2015 at 2:11 pm

One more head user in training still!

Don Thompson says

January 17, 2015 at 2:27 pm

20 gal., 2 – 4 people, no paper (special covered trash that gets changed often), a week if lucky….

Jim Allen says

January 17, 2015 at 2:41 pm

front 35 rear 15. I have gone 15 days with 4 people without pumping, but staying at marinas over night all but 3 of those days. I am in the great lakes, so no chance to dump at sea. No paper in toilets!!!

Melissa Feinmel says

January 17, 2015 at 2:59 pm

40 gals, 2 weeks, 2 people

Dave Skolnick (S/V Auspicious) says

January 17, 2015 at 9:01 am

2 people, 1 head, electric switchable between fresh and raw water. In NDZs we last a bit over a week including flushing paper (no problems). Outside of NDZs we use our Electroscan Type I MSD and go indefinitely.

Terry Peake says

January 17, 2015 at 3:32 pm

We don’t use our large holding tank. It’s easier to use our portable loo. Pump outs are not available in many places. We got the idea from aircraft systems.

Peter Robertson says

January 17, 2015 at 3:46 pm

1 head, 2 people, fresh water system, 2 tanks (10 + 20=30 gal. Cap.) 15 days w/paper & treatment… Add all the tankage you can is our rule

Ginny Teatro says

January 17, 2015 at 4:23 pm

15 gallon holding tank, 2 live aboard adult people not flushing paper, 7 days.

January 17, 2015 at 4:24 pm

15 gallon holding tank, 2 adults not flushing paper, 7 days max

Shelly Young says

January 17, 2015 at 5:05 pm

50 gal. 2 heads, 2 people

Jennifer Dean Neumann says

January 17, 2015 at 5:08 pm

30 gal holding tank. No paper. Fresh water electric heads. Two people with occasional drinks/ dinner guests. 10 days. MSD is on my wish list.

Annika Elias says

January 17, 2015 at 5:46 pm

2×13 gallon. 2 people about 1.5 weeks. We installed 2″ pvc pipes instead of soft hose, so we get 1-2 gallons more in the pipe and don’t have to waste water by flushing everything all the way to the tank each time. Just need to flush it a foot through the initial soft hose to avoid smells in the long run.

Tara Kelley Hemphill says

January 17, 2015 at 5:57 pm

2 people, 1 head, 15 gallons, no paper, 5-7 days. We just started 2 pump outs a week so no worries. We are at a marina.

January 17, 2015 at 1:05 pm

We have a 35 gal tank that will last us 2 for 2 wks. We do not put any paper in it. There are pumpout boats in Fl.

Mystic Knotwork says

January 17, 2015 at 6:13 pm

2 people, 15 gallons, and we are FT liveaboards. Well managed we can manage 2 weeks, but that’s pushing it (or not)

Michael R Miller says

January 17, 2015 at 7:21 pm

I see what you did there… ha

Windsong II says

January 17, 2015 at 3:01 pm

We have a 25 gal. holding tank. Two live aboard for 4 or 5 months of the year. We go 10 to 14 days without a pumpout, don’t worry about paper. We use regular “cheap” toilet paper.

To test it, put a bit of toilet paper in a glass of water, stir it up, if it turns to confetti it will work in a marine head. Have never had a clog.

We are in salt water and flush with seawater unless we are going to be away from the boat. Then we just use the shower to run fresh water into the head.

Our head has a macerator pump in the bottom so I think that accounts for no clogs. I think the electric macerator head uses less water to flush.

matty fletcher says

January 17, 2015 at 3:20 pm

‘Circe’ is an Australian 12 metre (40 foot) yacht with one man and a dog aboard in the marina, everything goes into the 350 Litre (90 us gallons) holding tank, salt water flush toilet including biodegradable paper, hand basin, shower and galley sink. I get approximately 3 weeks before pump out via a maceration pump 12 nm from land as per MARPOL. hope this helps.

Candy Ann Williams says

January 17, 2015 at 9:56 pm

Great idea for a post!!!

Yvonne McRobbie says

January 17, 2015 at 10:47 pm

Does anyone flush paper?

Neil Ingram says

January 18, 2015 at 1:54 am

100 gallon holding tank, fresh water, 45 to 60 days, Vacuflush system, single head.

Lupari Sue says

January 18, 2015 at 11:37 am

200 litres does us a couple of weeks. Full time live aboard.

ChrisW says

January 18, 2015 at 9:43 am

75 Gallon; three weeks, Single Lavac, NO paper (because of tank OB drain issues not head clogs). As Florida moves toward criminalizing safe and comfortable anchoring and demands proof of pump outs each week regardless of tank capability the whole thing many be moot.

Dave Tew says

January 18, 2015 at 3:53 pm

We have a portable but may go to a holding tank. Why is “no paper” important or a good practice?

Silvana Skoko Donald Stiff says

January 18, 2015 at 12:54 pm

No paper in toilet, fresh water flush…27 gal holding, 2 people and it lasts anywhere between 10-14 days when in marina, when out, then we shoot for 3 weeks. That is tough.

January 18, 2015 at 1:37 pm

200 gallon black water tank, 3 vacu flush heads, no paper, fresh water flush, mostly 2 aboard, generally go a month.

Jessica H says

January 18, 2015 at 5:18 pm

We liveaboard with two people. We live in a marina so #2 goes on shore and full-time jobs mean our heads are used less than those out cruising. We have a service that pumps our 50gal tank out once a month for $35. No marinas in San Diego offer pump out service to our knowledge. Some months we feel we are cutting it close. We installed a Phillippi tank monitoring system with ultrasonic sensors and that really takes the worry out of how full the black tank is. We use fresh water, no paper. The no paper concept may change when #2 is done aboard. This is a valuable topic! Thanks!

Lorie Eadie says

January 19, 2015 at 12:17 am

We need this info ! Ours is we think only 6 gals and with two of us its only good for a weekend ! With the two grandkids on board its less !

Marie H says

January 19, 2015 at 6:48 am

We are weekend boaters. We have two 35 gallon black water tanks. It’s usually the two of us with occasional guests and we can go easily a month between pump outs. We own our well, a “dockominium” and have a free pump out at our marina. We do have to move the boat to use it; so generally we go and do that before a trip out on the lake or on our way back in.

We do not put tp in the toilets. We’ve had too many friends that have had clogs and don’t want to have to deal with that mess. I just have conversation with the ladies about tp usage when they come aboard. We have flip top lid trash cans in each head. Hubby and I make the walk to the clubhouse for our morning constitutional; so generally it’s just liquid in our tanks.

January 19, 2015 at 4:33 pm

We bought a boat in New England 2 winters ago, the sale of course contingent upon a survey. The survey went well but the trip home down Buzzards Bay revealed the worst: a crack in the (full) holding tank. I suspect that the boat was not pumped out in the fall and the contents froze and cracked the tank while it sat on the hard during the winter. Several valuable lessons learned including “don’t buy a boat in the winter” but suffice it to say, we replaced EVERYTHING. Same size tank (16 gal) because that is what fit, new lavac toilet with electric pump (uses less water). Note: have rebuilt pump twice so far. Joker valves are VERY susceptible to crystalization. Now using 2 cups of vinegar thru pump once a month per mfg. So, 2 adults cruising full time. Husband pees discreetly (or not) over the side. We NEVER put paper in the system and we can go 5 or 6 days between pumpouts. If we can go ashore, we do and that stretches it to 6 or 7 days but then we MUST pumpout or go offshore. If we had it to do again ( God forbid!) I think we’d choose a composting toilet.

Charles Reynolds says

January 20, 2015 at 10:48 am

The Tall Ship I spent last winter aboard:

2x 100 gallon black water holding tanks. 3 Jabsco heads. No paper in the potties. Crew: 12-18 Use of shore-heads when reasonably possible.

Pump out about once per month, usually beyond the 3-mile mark on trips between ports. Never got to a point where tank capacity threatened overflow.

As a comparison, the 200 gallon grey water tank needed pumping every three days when shore-showers were available, every second day when not.

Charlie Jones S/V Tehani says

January 20, 2015 at 6:43 pm

WOW!! I have an MSD. 5 Gallons. with two aboard we commonly went 7 days. In Boot Key Harbor the boat came once a week. No problem. Now that I am single hand, I can easily do 14-15 days between pumps. NO liquids in the head, other than incidental.

One thing – in the Bahamas, I found ONE pump out facility- Paradise Island in in Nassau. Every where else was dump overboard, which I found amazing since the clear clean water is a major draw there

March 27, 2015 at 8:08 am

We have an Airhead composting toilet. 2 people, full-time liveaboards at a marina so go shoreside about half the time.

Pee-bucket, 2 gallons, gets emptied every other day or when pee shows through “danger-level” viewing window in pee-bucket.

You can tell when pee-bucket is getting close to full because of the pitch of the sound your urine makes trickling into the pee-bucket. It’s like how the sound changes when you’re filling a thermos and get close to the top.

Once a month or so I take a several garden-trowels full of used compost out of the poo-bucket and add back in new composting material. I replace about at about a 1:4 ratio, so 4 shovels out=1 shovel new composting material back in. This process takes less than 5 minutes.(These are my own rules. The Airhead instructions have you emptying the poo-bucket totally and using all new compost, but I find this easier and not at all gross.)

Soiled TP goes in poo-bucket. Urine-only TP and baby wipes go in lidded trash. If we weren’t shoreside, we’d need to maintain the poo-bucket +/- once a week rather than once a month. You know it’s time to deal with the poo-bucket when it gets hard to turn the compost stirring handle because the volume of composting material has grown.

Also, poo-bucket seems to like it if I sprinkle a teaspoon of “septic tank helper-germs” in there every now and then. It dramatically speeds up the process of TP turning into dirt. You can buy these in Home Depot.

Nothing bad has happened to us if I delay dealing with the poo-bucket for a few days, but the pee-bucket can overflow it you ignor its warning signs. Although this is to be avoided, it’s not NEARLY as awful as when a traditional holding tank breaks open and you flood the bilge with 40 gallons of raw sewage. Been there; done that; bought a composting toilet.

Kim Kattreh says

May 31, 2016 at 12:06 am

We pump out 1 time per week and we have a 40 gallon tank.

Paul Daniela Herlihy says

May 31, 2016 at 1:07 am

Two 18 gallon tanks. Family of three. We don’t wait until we are full to pumpout. If we are out for the weekend, we place a call for pumpout on Sunday evening so we are empty and ready for the following weekend. When out for the week, we pumpout whenever available and never wait until we are full. Here on the Mystic River, in CT, only one pumpout boat available… Not enough for the number of boats here. Local marinas offer this dock side service. All pumpout services are free in CT and RI. We tend to leave a tip.

Angel Mercer Ganey says

May 31, 2016 at 2:49 am

Nature’s Head installed this weekend. Will let you know how it goes….so to speak.

May 31, 2016 at 3:13 pm

Our boat had an 8 gallon holding tank which looked like it had never been used. The previous owner was a live aboard in a no discharge zone. Hmm. We replaced it with a 30 gallon. Very lucky to have dockside valet pumpout at our marina.

Robert Masse says

October 11, 2016 at 7:33 am

We just purchased a 45′ Trawler and it has a 45 gallon tank. Its just my wife and I and its being used as a liveaboard. We have 2 heads. Everything goes into the tank…no TP bucket. Our marina has dockside pumpout once a week. The prior owner of the boat I dont think took good care of the tank as we can only seem to go about 5 days until its full. We are attempting to clean it out now using treatments designed to clean out the tank and restore full capacity. We do have a sensor on the tank so we know when its full. Hopefully we can get it up and running to full capacity. I would love to be able to go 2 weeks + without a pumpout.

Susan DeMinico says

January 24, 2017 at 4:15 pm

We’re adding a gray water tank to a 39′ Avenger yacht that has never had a holding tank. (It’s been sitting for 10+ years.) Purchasing two composting toilets so no black water. My question is how big of a tank would we need to buy if we only wanted to pump out every two weeks? There will be two bathroom sinks, the galley sink and one shower (used occasionally.) Thanks so much for any advice!!

January 24, 2017 at 5:57 pm

Most places don’t require you to hold or pump out gray water, so we never have — and most boats don’t have gray water tanks. Assuming you are some place that prohibits dischanrging gray water overboard, so I decided to do some checking. Talking to some RV friends, they say to allow 6 to 8 gallons per day for a couple, assuming VERY short (1 minute) showers. Now, if you shower on deck, that would cut it some. That sounds reasonable to me — we figure 7 to 10 gallons of freshwater a day for the two of us and that includes our drinking and cooking water.

Since it seems that you are in some place with serious discharge rules, you may need a way to store the urine from the composting head. Two of us on board full time create a little over a gallon a day. If you can dump it ashore periodically, great, but if you’ll be in remote places, it’s something to think about.

August 26, 2017 at 11:51 am

We used to be able to go 2 weeks when we were in Sydney. Living aboard.

Mark Sidmore says

August 27, 2017 at 3:49 am

how long should a 40 gallon tank last 2 people?

August 28, 2017 at 11:10 am

Well, our 18-gallon will last about 4 days for two. But a lot depends on the model toilet you have and how much water it puts through per flush.

Beth Burlingame says

August 27, 2017 at 3:47 pm

We have an 80 gallon holding tank. Crazy, huh!

Not really . . .

August 28, 2017 at 12:22 pm

We have gone over a month between pumpouts, living aboard at the marina and mostly using the boat’s heads.

Blaine says

February 19, 2019 at 2:13 am

40 gallon tank, fresh water system, No prohibition on paper. Two aboard. When dockside average is a week and a half. Underway would be a week..

Jonathan says

February 4, 2020 at 5:48 pm

I just pump my holding tank into my neighbors.. oh wait.

More seriously… I have a 30 gallon.. pump it out once a month, as it’s just me and I’m not a full time live-aboard.

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How do I empty my black water tank?

• Thread starter cecho
• Start date Mar 12, 2013

Petty Officer 1st Class

• Mar 12, 2013

The tank is up front and the hose that it's supposed to be emptied with exits the hull a good 4 feet above it which makes gravity not an option.  

Master Chief Petty Officer

Re: How do I empty my black water tank? Pump out at the marina is what I do. LK  

Re: How do I empty my black water tank? With the current drought, the service area at the marina at the lake I frequent is not currently accessible by boat. Is there an at-home option? I guess I could always go to the other local lake every time I need to pump out the boat. :lol:  

Re: How do I empty my black water tank? Is there a RV/trailer(5th wheel etc..) park close by? They pump those out too....... Maybe for a small fee they'll let you pump out....  

smokeonthewater

Fleet admiral.

Re: How do I empty my black water tank? to empty at home you will need to purchase a macerator pump and whatever valves, fittings, hoses, and containers you deem fit to properly dispose of it.  

WIMUSKY said: Is there a RV/trailer(5th wheel etc..) park close by? They pump those out too....... Maybe for a small fee they'll let you pump out.... Click to expand...

Re: How do I empty my black water tank? Thanks, I'll call the marina and check on using a trailer to do it. If that isn't an option I'll go the pump route.  

cecho said: With the current drought, the service area at the marina at the lake I frequent is not currently accessible by boat. Is there an at-home option? I guess I could always go to the other local lake every time I need to pump out the boat. :lol: Click to expand...

Re: How do I empty my black water tank? haha. This is my first black water tank. I'm guessing it's 20 gallons or so. I didn't realize you can do it that infrequently. I just thought you'd want to get that crap outta there ASAPee.  

smokeonthewater said: rv's are gravity drain... no pumps involved..... Click to expand...

WIMUSKY said: Now that you mention it, duh...... And here I thought I had a great idea, o'well....... Click to expand...

frantically relaxing

Senior chief petty officer.

Vice Admiral

• Mar 13, 2013

Alwhite00 said: How often do you need to pump it out? What the heck is going on on your boat? How big of tank do you have? I pump out in the middle of the season and again right before it goes into storage. LK Click to expand...

25thmustang

Lieutenant commander.

Re: How do I empty my black water tank? I pump mine as much as possible. At least a few times a season, but for my sized boat it's a smaller tank (larger than original). If you have a thru hull and macerate you can pump it from below and dispose of it in a land septic or sewer. It's a gross job though!  

Re: How do I empty my black water tank? We do not use the head for "solids" if you catch my drift and have never had a problem with odor. I put that chemical in it for odor (forget the name) and so far, so good. Head is fresh water supplied from the freshwater holding tank. LK  

Chief Petty Officer

Alwhite00 said: We do not use the head for "solids" if you catch my drift and have never had a problem with odor. I put that chemical in it for odor (forget the name) and so far, so good. Head is fresh water supplied from the freshwater holding tank. LK Click to expand...

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Bleach in water tanks

• Thread starter NYSail
• Start date Jul 3, 2021
• Forums for All Owners
• Ask All Sailors

Hello all. So every season I thoroughly clean my water tanks using bleach with several good rinses. This also includes running the mixture into all hoses and letting sit. Water tanks are clean and I have no issue using it for drinking / cooking. A friend does same however he also adds 2/3 tsp of bleach per 8 gallons when he fills up. How many folks do this…… doesn’t seem like a bad idea to keep things non toxic just in case. Btw for drinking we do run the water through a “Epic Water filter” Thanks greg  

If the water is coming from a reliable municipal supply, I don't think adding bleach adds much. Flush the hose before filling. If the water source was somehow suspect, then perhaps. Replace the O rings on the fill caps, when they deteriorate water from the deck can enter the tank. That would be a cause of contamination.  

The first and only time I commissioned our water tanks was when we took possession from the PO in 2002. I also alternate tank use after each fill up. Never added bleach to a fill up. Water tastes fresh and odor free to this day.  

If the water comes from a municipal supply, it may already contain chlorine. Adding more can make you sick. Our Washington State Health folks say to add one teaspoon of bleach per gallon of cold water and leave it to sit for 40 minutes, then flush well. I usually do this annually. Make sure to flush the hot water heater as well to get the bleach taste and smell out.  

dlochner said: If the water is coming from a reliable municipal supply, I don't think adding bleach adds much. Flush the hose before filling. If the water source was somehow suspect, then perhaps. Replace the O rings on the fill caps, when they deteriorate water from the deck can enter the tank. That would be a cause of contamination. Click to expand

I do not like the taste of Cl so I avoid adding it after cleaning. A water filter is a good idea for drinking depending upon where you are. If you are typically filling at a reliable source, then not needed, but if you travel and may have unknown reliability, then a filter seems like a really good idea. I prefer not to chlorinate my water. dj  

For under $20 on Amazon you can get a Total Dissolved Solids meter which will yield an estimate of how clean the water is. It won't assess pathogens, however if the water has low TDS levels and it is from a municipal source it is likely safe.  

Sanitize my tanks annually as per instructions from Peggy Hall's book. Bleach is added to filled tank and allowed to circulate and remain in lines for 8 hours. Tank is then emptied and wiped clean, refill tank with filtered municipal water, after water hose is allowed to run for about 5 minutes prior to inserting it into deck fill. Diluted bleach solution is finally flushed from onboard water lines. I do not add additional chlorine to the water after the tanks are refilled. Have never had an issue and water is clean with no odor. I usually have bottled water onboard for drinking, same as at home.  

I usually add a splash of bleach to each 30-gallon tank when I fill it. I don’t turn the water over fast enough, and I found that by the time I switched to a full tank, it was a little “skunky”, particularly in the hot summer. I don’t drink the water, but I do brush my teeth and wash dishes with it. I can smell a faint hint of chlorine, but it is preferable to the skunky smell I get without the bleach. I could use one and refill it twice as often, and maybe I wouldn’t need the disinfectant, but I haven’t tried that yet. Greg  

First, what is your tank made of? if its aluminum then bleach is the last thing you want anywhere near it. Clean the pipes with bleach, as per Peggy but not aluminum tanks.  

Good point…mine are plastic. Greg  

Plastic tanks. And like I said I clean them once a year with bleach including the lines with a great flush. I also use my water extensively so it never sits for long periods. I’ve never had a problem with bad water I was just interested when my friend told me that he puts bleach in his. Thanks for all the responses guys!  

We do the Peggie‘s shock treatment every Spring when we launch. Use 4oz. of bleach per 10 gallons of water. Run the taps to fill the lines and till you can smell the bleach. Let it sit for no more than 24hrs. Then dump the tank, flush it out, then refill.  

Peggie Hall HeadMistress

So many of you have misquoted important parts of the fresh water recommissioning instructions from my book that I'm posting those instructions here: Although most people think only in terms of the tank, the plumbing is actually the source of most foul water, because the molds, mildew, fungi and bacteria which cause it thrive in damp dark places, not under water. Many people—and even some boat manufacturers—believe that keeping the tanks empty reduce the problem, but an empty water tank only provides another damp dark home for those “critters.” There are all kinds of products sold that claim to keep onboard water fresh, but all that’s really necessary is an annual or in especially warm climates, semi-annual recommissioning of the entire system—tank and plumbing. The following recommendations conform to section 10.8 in the A-1 192 code covering electrical, plumbing, and heating of recreational vehicles (which includes boats). The solution is approved and recommended by competent health officials. It may be used in a new system a used one that has not been used for a period of time, or one that may have been contaminated. Before beginning, turn off hot water heater at the breaker; do not turn it on again until the entire recommissioning is complete. Although most people think only in terms of the tank, the plumbing is actually the source of most foul water, because the molds, mildew, fungi and bacteria which cause it thrive in damp dark places, not under water. Many people—and even some boat manufacturers—believe that keeping the tanks empty reduce the problem, but an empty water tank only provides another damp dark home for those “critters.” There are all kinds of products sold that claim to keep onboard water fresh, but all that’s really necessary is an annual or in especially warm climates, semi-annual recommissioning of the entire system—tank and plumbing. The following recommendations conform to section 10.8 in the A-1 192 code covering electrical, plumbing, and heating of recreational vehicles (which includes boats). The solution is approved and recommended by competent health officials. It may be used in a new system a used one that has not been used for a period of time, or one that may have been contaminated. Before beginning, turn off hot water heater at the breaker; do not turn it on again until the entire recommissioning is complete. Icemakers should be left running to allow cleaning out of the water feed line; however the first two buckets of ice—the bucket generated during recommissioning and the first bucketful afterward--should be discarded. 1. Prepare a chlorine solution using one gallon of water and 1/4 cup (2 oz) Clorox or Purex household bleach (5% sodium Hypochlorite solution ). With tank empty, pour chlorine solution into tank. Use one gallon of solution for each 5 gallons of tank capacity. (Simpler way to calculate: 1 quart bleach/50 gal water tank capacity) 2. Complete filling of tank with fresh water. Open each faucet and drain cock until air has been released and the entire system is filled. Do not turn off the pump; it must remain on to keep the system pressurized and the solution in the lines 3. Allow to stand for at least three hours, but no longer than 24 hours. 4 Drain through every faucet on the boat (and if you haven't done this in a while, it's a good idea to remove any diffusion screens from the faucets, because what's likely to come out will clog them). Fill the tank again with fresh water only, drain again through every faucet on the boat. 5. To remove excess chlorine taste or odor which might remain, prepare a solution of one quart white vinegar to five gallons water and allow this solution to agitate in tank for several days by vehicle motion. 6. Drain tank again through every faucet, and flush the lines again by fill the tank 1/4-1/2 full and again flushing with potable water. An annual or semi-annual recommissioning according to the above directions is all that should be necessary to keep your water tasting and smelling as good as anything that comes out of any faucet on land. If you need to improve on that, install a water filter. Just remember that a filter is not a substitute for cleaning out the system, and that filters require regular inspection and cleaning or replacement. To keep the water system cleaner longer, use your fresh water...keep water flowing through system. The molds, fungi, and bacteria only start to grow in hoses that aren't being used. Before filling the tank each time, always let the dock water run for at least 15 minutes first...the same critters that like the lines on your boat LOVE the dock supply line and your hose that sit in the warm sun, and you certainly don't want to transfer water that's been sitting in the dock supply line to your boat's system. So let the water run long enough to flush out all the water that's been standing in them so that what goes into your boat is coming straight from the water main. Finally, while the molds, fungi and bacteria in onboard water systems here in the US may not be pleasant, we're dealing only with aesthetics...water purity isn't an issue here--or in most developed nations...the water supply has already been purified (unless you're using well-water). However, when cruising out of the country, it's a good idea to know what you're putting in your tanks...and if you're in any doubt, boil all water that's to be drunk or used to wash dishes, and/or treat each tankful to purify. It's even more important in these areas to let the water run before putting it in the tank, because any harmful bacteria will REALLY proliferate in water hoses left sitting on the dock. These are not MY instructions...I found them in the owners manual for a 1985 Sea Ray I owned...you can also find them on most of the RV sites. People have expressed concern about using this method to recommission aluminum tanks. While bleach (chlorine) IS corrosive, it’s effects are are cumulative. So the effect of an annual or semi-annual "shock treatment" that's completely flushed out of the tank within a few hours is negligible compared to the cumulative effect of holding chlorinated city water in the tank for years. Nevertheless, it's a good idea to mix the total amount of bleach in a few gallons of water before putting it into either a stainless or aluminum tank. People have also expressed concern about the potential damage to rubber and neoprene water pump parts. Again—the cumulative effect of carrying chlorinated water is far more damaging over time than the occasional “shock treatment.” And it’s that cumulative effect that makes it a VERY bad idea to add a little bleach to each fill. Not only does it damage the system, but unless you add enough to make your water taste and smell like a laundry, it’s not enough to do any good. Even if it were, any “purifying” properties in chlorine evaporate within 24 hours, leaving behind only the corrosive properties. --Peggie  

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