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Plumbing Fixtures on Boats

With seafaring ancestors in her maternal line, Liz gives them credit for her lifelong fascination with boats and water.

A motor yacht with full living facilities has plumbing to be aware of

A motor yacht with full living facilities has plumbing to be aware of

How Boat Plumbing Differs

Boat plumbing differs from household plumbing, and even to some extent from that aboard a recreational vehicle (RV). Many articles have been written about plumbing in a house with regard to fixing problems and general maintenance, and a few have addressed the RV'ers.

Boats, however, are yet another "animal." Aboard a boat large enough to have cooking, bathing and toilet facilities, there are three different ways the plumbing is handled and routed, and three different ways used for dealing with waste water.

Fresh Water Storage Tank

The first storage tank I will address is the freshwater tank. This is filled only with potable (drinkable) water from a city water supply or well. Some may argue that since most don't drink the water from the faucet on a boat, as it is mainly used for washing, it doesn't matter. However, do you want to wash your dishes in water unsafe to drink? I don't.

Depending on the size of the boat, this tank can range from 20 gallons (what we had on our boat), upwards to extreme limits. Large cruise ships may have freshwater tanks holding thousands of gallons. I don't know for certain, but I'm guessing it is possible that these days, some of the largest ships may have on-board de-salinization plants to create fresh water as needed.

Again, depending on the size of the boat, the tank, and level of luxury, there may or may not be a gauge indicating the level of the water left. On our boat, it was guesswork.

Water From Another Source

On a boat, only the sink and shower draw from the freshwater tank. The toilet uses a device called a sea-cock. This is a special valve that draws in the water directly from the water in which you are boating.

The sea-cock has a built-in mesh filter to prevent drawing in debris that could foul the pipes or add unnecessary burden to the holding tank. It must be checked on a very regular basis for proper operation, and the valve must be able to turn easily. If it is frozen, or hard to turn, have it replaced ASAP!

Each time you return from a trip, be sure to close it fully.

Because this is a direct line to the water in which the boat sits, it holds potential for disaster. Boats have sunk due to being flooded by a faulty sea-cock. Even though, like a faucet in your home, the water in an open sea-cock valve is not supposed to begin flowing until there is a demand (i.e. flushing the toilet), do remember that things can break or wear out.

Can you imagine the nasty mess of finding your boat riding up to the gunwales (pronounced "'gun'uls") in water, awash not only in sea or river water, but also in the upwelling contents of the holding tank from out of the toilet? If you have a small leak, the bilge pumps may handle it--for a while, but if there is a major malfunction, they will not be able to keep up.

The sea-cock and bilge pumps are the single most important pieces of plumbing equipment to have in good working order.

A seacock will generally be this type of valve on smaller yachts and pleasure boats Shown in closed position

A seacock will generally be this type of valve on smaller yachts and pleasure boats Shown in closed position

You don't want to find your boat awash up to the gunwales!

You don't want to find your boat awash up to the gunwales!

Gray Water: The Sink

On most pleasure crafts, gray water is handled in two ways. I'm going by what was on our boat, but it's probably fairly typical of small yachts.

The water from the galley sink was routed directly overboard through a small port right behind the sink. The drainage from the sink had the standard P-trap underneath, just as is found in homes and RV's, but instead of connecting to a sewer line or routing into the holding tank, it simply went out the side of the boat and into whatever body of water you were cruising.

Gray water is not harmful, and on board a boat, you are required to use specifically made biodegradable soaps and detergents for this very reason. That way, it breaks down easily and does not harm wildlife, or create algae blooms.

The main difference between boats and RVs here is that RVs have separate gray water holding tanks, as you cannot be discharging waste water as you go down the road, or at your campsite.

Gray Water: The Shower and Bathroom Sink

The shower is similar but handled in a slightly different way. On many smaller yachts (up to about 30 feet in length), the shower is positioned right above the toilet. When using it, you must be sure the toilet lid is closed, so you do not prematurely fill up your black water holding tank.

The shower drain in the floor routes the water back into the bilge where the bilge pumps pick it up and toss it overboard. Like the sink, then, the shower water goes out to the body of water, but via a different means.

The washbasin also routes back to the bilge.

So, you must likewise shower and wash up with special biodegradable soaps, usually marked as containing 'no phosphates.'

Black Water: The Ugly Stuff

The holding tank from the toilet is separate from everything else. For obvious health reasons, it is illegal to dump black water overboard.

However, on the water, you cannot simply pull up to a dump station, open a valve, and use gravity to dump contents via a hose into the land-based holding tank.

Instead, there are docks with pumping stations. In the majority of cases, this is strictly a do-it-yourself operation. The pump-out station operators may offer help or instructions for newbies, but you are basically on your own.

A typical pump-out station. Dockside pump-out stations are self-service.

A typical pump-out station. Dockside pump-out stations are self-service.

It's Self-Service, Folks!

You pull up dockside and attach the screw-in hose from their pump to your pump-out port. Next, you pull in a freshwater hose through the porthole (that's a window for non-boating folks) and aim it down the toilet. Turn on the water, and turn on the pump. The pump-out hose is often a clear material, and you can see when it is no longer pumping out waste but clear water. If the hose is opaque, listen for a change in the pitch of the pump that will tell you it's done. Turn off the water, and pump a little more, so your tank is not full of water.

Disconnect the pump-out hose and replace the cap on the pump-out port. The toilet uses chemicals as in an RV, to both help break down solids and control odor; at this point, refill the chemical into the holding tank via the toilet, as per the dosage directions on the bottle. All done!

Some areas provide free pump-out service; others charge a fee.

Maintenance of Boat Plumbing

More than any other situation, maintaining everything in good working order aboard a boat is vital. Even in an RV, you can drive to a repair shop. Not so with a boat.

Plumbers don't make calls out on the water. Nothing, but nothing would be more maddening, inconvenient, and possibly dangerous than to be stuck out in the middle of a remote waterway with plumbing problems.

Check all systems for proper operation each time you use your boat, and nip any problems in the bud. Make sure you schedule maintenance days, where you can go over everything with no rush to get underway, and you will have many happy and trouble-free times out on the water.

© 2011 Liz Elias


HaremCinema on December 27, 2019:

This was interesting. More people should get to try boating.

Liz Elias (author) from Oakley, CA on December 10, 2014:

Hello, poetryman6969,

LOL! True, not everyone is "boat-minded." I do miss our boat; it was fun, but the old saying of "a boat is a hole in the water surrounded by wood (or fiberglass, these days), into which you pour money" was pretty true.

Even normal maintenance parts, once you put "marine" in front of the name of the part, the price goes way up. Then, the docking fees, if your boat, (like ours was), is too big to trailer, and the inflated prices for fuel at the gas docks. It all adds up.

On the other side of the coin from your comment is the fact that there are plenty of people who have boats, and who should not. There are many idiots driving about on the water, just as they do on the road. Just because you can afford a boat, does not mean you should buy one, in those cases!

Thanks much for stopping by; I'm pleased you enjoyed the article.

poetryman6969 on December 10, 2014:

It confirms my impression that boats are for other folks but interesting nonetheless!

Liz Elias (author) from Oakley, CA on September 06, 2011:

@ Simone- Hi there! Thanks so much. Nice to know I was able to provide useful info...appreciate the comment!

@Robin- Hello! Thanks so much for stopping by and leaving a comment. ... LOL.. lack of a place to 'go' would be my main problem with a speedboat. I'm not into trying to sit on a coffee can or hanging over the side. ;-)

... As long as everything is taken care of, problems don't normally happen. Glad you found the article interesting.

Robin Edmondson from San Francisco on September 06, 2011:

Very interesting! I always wondered how this was done. I think we'll just stick to speed boats where there isn't a bathroom; I'm not good at plumbing issues in the house, so a boat's plumbing would really be difficult! Thanks for the informative Hub!

Simone Haruko Smith from San Francisco on September 06, 2011:

I've been curious about this for ages, so I really enjoyed reading this Hub! The black water tank... gosh... blehhh... but it's smart that they've got it separated out. Goodness, it's fascinating how boats work. Thanks for sharing the fab explanation!

Liz Elias (author) from Oakley, CA on September 05, 2011:

Hello, PenMePretty!

Thanks so much for your kind comment and the votes! Come back any time.


PenMePretty from Franklin on September 05, 2011:

With all your knowledge...I want you to be on the boat with me. please. VOTED up, interesting, useful.

Liz Elias (author) from Oakley, CA on September 04, 2011:

@K9--thanks so much for all the votes and great comment. I kind of miss our boat--and kind of not. The downside was, it amounted to taking all the housework with you at playtime. We sold it a few years back, after it sat most of the year without being used, and no extra money for the inflated gas-dock prices--why keep paying slip fees?

@Will Starr..thank you very much! Glad you liked the article.

WillStarr from Phoenix, Arizona on September 04, 2011:

Informative Hub!

India Arnold from Northern, California on September 04, 2011:

What a great hub! You are spot on with one DML! Our boat had full facilities and it can be trouble if you don't know how to manage it. We were fortunate to have a brother who is very savvy at everything having to with a boat, inside and out. Nothing is worst than not having boat plumbing know-how when it comes to playing on the water! Nautical plumbing, as you say, IS a whole other animal! Up and all across the board!