I think we've solved it, David...
I'd guess that fewer than 10% of boats have waste tank vents that can be closed...that yours really does has to mean that the boat has either done some serious passagemaking, or the owner who installed the valve planned to. If the vent IS open and the pickup is on the top of the tank, the pickup tube has to be the culprit.What's the tank made of? If it's metal--and/or the pickup tube is--urine has most likely either perforated it or eaten through it enough to cause it to fall off. The tank is most likely in bad shape too. So you want to check the inside of it thoroughly after you get it empty...which, btw, you can do by sticking the pumpout hose into the tank via the inspection port. Send plenty of water down the deck pumpout fitting while pumping out to rinse out the tank.yIf the tank is plastic, the tank should be ok...and SHOULD have a PVC pickup tube that's apparently broken loose from the fitting. It's a relatively easy fix...cement a new pipe inside the thread-barb tank fitting. Again, rinse out the tank thoroughly before starting any work.If the tank is fiberglass, the inside of it should be inspected for blisters, rot etc.No matter what the tank is made of, if the tank fittings and/or pickup tube are metal replace 'em with plastic. Metal and waste are a very bad combination.