I have dealt with the same problem on my
boat.
Start with the
tanks. Does it smell like
holding tank water? If so you know where to start looking. Either way, access the
tanks and look for leaks at the tanks and around the pressure
pump and
water heater. Obviously check with the system pressurized. While we are at it turn off the pressure
pump and see if that has an impact.
If it is not leaking from inside, some things I have addressed on Cynosure- re-bedding the
genoa tracks and where the
chain plate goes through the
deck. If there are issues with these, check for
core rot in the surrounding
deck area.
None of thar
repairs are that difficult just a PITA.
Bill