How To Pump Out Your Holding Tank

How To Pump Out Your Holding Tank | Life of Sailing

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.

How To Pump Out Your Holding Tank
Capt Chris German

Capt Chris German

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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