Common problems with Thetford toilets include leaking seals, leaking valves and problems with the tank level indicator. Most recreational vehicle manufacturers install these toilets in their products. The bowl of the toilet has a blade seal that retains water in the bowl after flushing. If the water leaks around the seal, odors can enter the bathroom from the blackwater holding tank.
With a Thetford toilet, the user must hold the valve open for a few seconds after the blade closes to add about an inch of water to the bowl. If that water disappears between uses, something has damaged the seal or is preventing the blade from closing completely.
Repairing the blade seal requires removing the toilet from the RV. These toilets seal the connection to the tank using a rubber ring instead of the wax seal common with home toilets. After replacing the seal, the owner should pour about four cups of water into the bowl and check for leaks before reinstalling the toilet.
Leaking water valves allow the water to continue to run after releasing the handle. Replacing the valve with a new one is the easiest way to repair the problem.
Sometimes the materials in the holding tank cause the indicator gauge to stick, even when the tank is empty. To repair this problem, pour a couple of trays of ice cubes in the tank, and take the RV for a drive. The moving ice loosens the float so the indicator works correctly again.