Just water?
Jay, is it clear water, or backflow from the holding tank? I've had the latter problem with a Groco, but only after sailing in moderate seas (the more empty the holding tank, the more wave action needed). I replaced the joker and flapper valves with maybe slight improvement. The next suspect is typically the vent line. Mine appears to be unclogged. If you are certain you are pumping long enough, then what? After that, I guess we have to buy Peggy's book (available at the Chandelery)!
