Boat owners who've never read the installation instructions for their manual toilet never realize that they're missing something very important in their installation: a vented loop in the intake. It needs to be at least 6-8" above waterline AT MAX HEEL, which on most sailboats puts it 2-3 FEET above the bowl. It doesn't go in the intake line between the thru-hull and the pump, it belongs between the pump and the bowl, which requires replacing the short piece of hose used by toilet mfrs with 2 pieces of hose long enough to put it high enough. All manual toilet installation instructions include a drawing showing its location.
A vented loop in the intake does several things that save boat owners from themselves: it breaks the siphon started by pumping and prevents water OUTside the boat from seeking its own level INside the boat via the toilet bowl when the thru-hull is left open and/or the wet/dry lever is left in the wet position. Failure to have the vented loop is the reason your toilet is filling when you aren't aboard and have left the intake thru-hull open...and it's often the reason why boats sink in their slips.
And btw...boatbuilders, who are the WORST sanitation plumbers on the planet, often install the vented loop, but put it under the vanity which renders it useless.
--Peggie
A vented loop in the intake does several things that save boat owners from themselves: it breaks the siphon started by pumping and prevents water OUTside the boat from seeking its own level INside the boat via the toilet bowl when the thru-hull is left open and/or the wet/dry lever is left in the wet position. Failure to have the vented loop is the reason your toilet is filling when you aren't aboard and have left the intake thru-hull open...and it's often the reason why boats sink in their slips.
And btw...boatbuilders, who are the WORST sanitation plumbers on the planet, often install the vented loop, but put it under the vanity which renders it useless.
--Peggie
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