I am assuming that the flexible tank which is about 24" * 24" is the waste tank. Does anyone know where you can get a new one, it looks like it may be leaking
That's a fresh water tank you're lookin' at... The vent is a hole drilled into the bronze fill plug and any water likely came from that. Bertram never fitted the B31 with waste tanks.
The strange thing is there is a square fiberglass tank in front of the collapsible one. And it appears that the drain lines from the head go into the collasable one. I have to see what goes into the permanet mounted glass one.
Sounds like some previous owner moved the fiberglass water tank forward and added a bladder style holding tank.
The water tank has a 1/2" outlet at the bottom, center, aft & a 1" bronze fill hole on top, plugged with a square head plug. The plug is where the vent is drilled.