The PO of my boat claimed he never used the head. I assumed the holding tank must be empty. I've had some issues with backflow into the bowl, but I have not yet checked the joker vavle. I know the system has at least a gallon or 2 of water in it. Went to pump the tank (vacuum system) out and nothing is coming out. I have not checked the vent yet because I don't know where it is located on a 270. I would have thought the tank would still vacuum out even if the vent was blocked, but can't verify this.
Thoughts
Thoughts