While we were in Mexico our holding tank started to give us trouble. Once in a while it wouldn't pump out and at other times it did just fine. We always use it in anchorages and marinas for obvious reasons. On the bash up we turned the y valve to overboard but when we got back to SD when I tried to pump out the residual in the tank it jammed up solid. It wouldn't pump out at the dock or even the overboard discharge. I used some acid to try to brake up the clog but it appears that all that did was cause all of the built up salt muck on the sides of the tank and hoses to come loose and fall to the bottom and really jam things up. I finely got my space suit on and rubber gloved myself almost to death and "dived" into the project. I found the problem when I discovered that an old tank level sending unit from the the old system broke off and fell to the bottom of the tank. Gee, it was just the right size to get caught in the out fall hose. I mean exactly the right size by an eighth of an inch. I've got everything clear now except the hose from the Y valve to the tank. That's jammed up now and I suppose that's from the acid bath. I ran out of time so I'm going to have to do it all over again tomorrow. How much fun can a boat owner have anyway? At least it waited until I got back to a slip.