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Marine Toilet Maintenance

Modern marine toilets require minimal maintenance, but ignore them completely at your own peril.

Cleaning the Lines

Marine Toilet Maintenance

Heads flushed with salt water accumulate scale deposits in the discharge channels and hoses. Scale deposits cause a head to get progressively harder to flush, and it is scale on the valves that allows water in the discharge line to leak back into the bowl. Calcium deposits eventually lead to total blockage, a most unpleasant prospect.

Avoiding this problem is as easy as running a pint of white vinegar through the head once a month. Move the vinegar through the head slowly, giving the head a single pump every 4 or 5 minutes. The mildly acidic vinegar dissolves fresh scale inside the head and hoses. When the vinegar has passed all the way through the system, pump a gallon of fresh water through to flush the lines.

If you suspect you already have a scale build-up, dissolve it with a 10% solution of muriatic acid, available from most hardware stores. The acid won't harm porcelain, plastic, or rubber parts. It does attack metal, but consequential damage takes a long time. The biggest danger is to eyes and skin, so be sure you observe all label precautions.

Pour two cups of acid into the bowl. It will fizz as it reacts with the calcium deposits on the bowl valve. When the fizzing stops, pump the head — intake closed — just enough to empty the bowl. This moves the acid into the pump. After a few minutes pump again to move the acid into the discharge hose. Let it sit a few more minutes before opening the intake and thoroughly flushing the toilet and lines. The acid is "used up" as it reacts with the calcium, so heavy scaling may call for more than one treatment. Scale and salt also find their way into the anti-siphon valve in the discharge line. Remove the valve and soak it in warm, soapy water to dissolve deposits that could be holding it shut or open.


To keep the pump operating smoothly, follow your monthly vinegar flush with a dose of oil. The best choice is a lubricant intended for marine toilets, but you can also use mineral oil. Oil lubricates the pump wall and helps to keep internal rubber and leather parts supple.

The usual treatment is to let a little water into the bowl, pour in a couple of ounces of lube, and pump this through the toilet. This method is adequate, but less than ideal because it lubricates only the discharge side of the pump. To also lubricate the intake side, disconnect the intake hose from the closed seacock and pour the oil into this hose. Pumping the head will pull this oil through both chambers of the pump.

While you are servicing the head, lightly coat the piston rod with Teflon grease. This will prolong the life of the piston-rod seal.


Marine toilets need not stink, but they often do. The discharge hose is, by far, the most common culprit. To check yours, rub the hose with a damp, clean cloth, then sniff the cloth. If it has picked up an odor, the hose is permeable and you will never eliminate the odor until you replace this hose with proper sanitation hose.

Leaking connections are another source of odor, and you can use your cloth the same way to locate a leak. Also check the seal around the piston rod. On some heads, tightening the seal will stop a leak; on others a leaky piston-rod seal must be replaced.

Another common source of head odor is grass and other marine life trapped inside the flush-water passage under the rim of the bowl. Prevent this by installing a strainer in the intake line.

An anti-siphon valve in the discharge line can also release odors into the boat. A properly installed valve vents outside the cabin area.


If the toilet gives off a foul odor but it isn't leaking, if it is difficult to pump but the discharge hose isn't clogged, or if it just isn't working right, it is time for an overhaul. The exact procedure for rebuilding your head will depend upon the make and model, but marine toilets are simple machines and you are not likely to encounter many difficulties. Rebuild kits are available that contain new valves, springs, gaskets, and often screws — in short, everything you need to recondition the toilet. The kit will also provide a detailed instruction sheet.

What the instruction sheet may not tell you is that overhauling a toilet is always more pleasant and nearly always easier when you remove it from the head compartment before taking it apart. It may also fail to instruct you to lay out the parts in order as you dismantle the toilet so you will know which screws go where, or how each valve should be oriented.

A few general rules apply to virtually all manual toilets and may help you to avoid problems:

  • Weighted flapper valves always have the weight up, and flapper valves always open to give the least restricted flow, i.e., they should always be oriented so the widest opening faces the outlet.
  • The bill on a joker valve always points in the direction of the flow.
  • The walls of the pump cylinder should be polished clean and lubricated lightly with petroleum jelly.
  • If the piston uses leather cups, two are required facing opposite each other.
  • Clean all mating surfaces thoroughly of old gasket or sealant.
  • Use sealant on all gaskets to prevent them from weeping.
  • When you reattach the bowl to the base, tighten the four nuts evenly and not too tightly or you will crack the china.
  • Wait until you have reinstalled the head to tighten the pump rod seal, then tighten it only enough to keep it from leaking.

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Don Casey

Contributor, BoatUS Magazine

Don Casey has been one of the most consulted experts on boat care and upgrades for 30 years, and is one of the BoatUS Magazine's panel of experts. He and his wife cruise aboard their 30-footer part of the year in the eastern Caribbean. His books include Don Casey's Complete Illustrated Sailboat Maintenance Manual, and the recently updated This Old Boat, the bible for do-it-yourself boaters.