I have a livewell on the port side behind the companion seat. (95 Islander). We use the well to store our catch and keep them alive until returning to dock. (Fluke, seabass). I have a baitwell pump connected and run it occasioally to fill with O2 water but it quickly drains out the fill tube when the pump is off. We don't run the pump contiuously to reserve house battery power for electronics. Is there a check valve that could be cut into the supply line to prevent backflow draining to the pump? Other solutions to the draining problem? We do cork the thruhull fitting in the bottom. I know I could close the seacock but that would be a pain to do each time I want to run the pump, maybe every 1/2 hour or so.