Hired a guy to pump out our mess. He could only get out 20 or so gal. Thought it was a vent hose problem. WRONG!! Ended up replacing all hoses, new pump & cleaned the tanks. I found LARGE pieces of plastic in the hoses, pump & tank. Tried rebuilding the pump, no bueno. HAIR - LONG HAIR was in everything.
What I suspect is the PO'S sent the hair down the crapper along with some broken plastic. The plastic & hair jammed the pump bad. Back flushing didn't work. While the guy was here we tried running the pump in the overboard side. That's when we realized the system was FUBAR.
I wanted to take a hammer to something - they weren't around.