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Solved problems · Plumbing · Crew answer

Why does my marine toilet bowl fill up with water by itself?

A bowl that slowly fills or overflows is usually siphoning seawater because the vented loop is missing, clogged or stuck. This can sink a boat, so close the seacocks first.

Symptom

Seawater rises in the toilet bowl between uses, sometimes to the rim, or the bowl refills when the boat heels.

Likely cause

When the toilet sits near or below the waterline, seawater can siphon in through the intake or back through the discharge. A vented loop (anti-siphon valve) at a high point in the hose breaks that siphon. If the loop is missing, mounted too low, or its small valve is crusted shut, and the pump's valves are worn, water keeps flowing in. Jabsco calls for the loop to be at least 20 cm (8 in) above the highest possible waterline.

Stop now if

Water is overflowing the bowl or rising in the bilge. Close the toilet's inlet and discharge seacocks immediately and pump the bilge. If water still comes in, treat it as flooding and call for help.

The fix, in short

  1. Close the seacocks. Close both toilet seacocks whenever the head isn't in use, and always when you leave the boat.

  2. Find the vented loop. Trace the intake hose from the pump to the bowl and the discharge hose. The loop should sit well above the waterline even when heeled, and on the correct hose. Fitting it between the seacock and pump is a common mistake that lets the pump suck air.

  3. Clean or replace the valve. Unscrew the small valve at the top of the loop and soak it in warm water or vinegar to clear salt crystals, or replace it. Never plug or cap it to stop it weeping.

  4. Service the pump valves. Worn joker and flapper valves let water past. Rebuild the pump with the maker's service kit.

  5. Raise a low loop. If the loop is too low, rerun the hose so the loop sits higher, following the toilet manufacturer's installation instructions.

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Marine toilet: Manual or electric marine toilet, intake and discharge seacocks, vented loops and hoses

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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