I saw the post regarding the mystery water leak. The comment that the toilet bowl was full to the brim, may be a clue. On our trawler cat, occasionally, the toilet would over fill, particularly when the fresh water tank was full. On our boat, there is a solenoid that controls the water into the toilet. If the solenoid is below the water tank (or below the water level in the tank) and the solenoid sticks open, then you can get a siphoning effect causing the bowl to overflow. We fixed that issue by moving the solenoid above our water tank.