[jergofish]

No, it is not cool to have a bilge pump through hull exit under water! My 215 has the exit high up on the transom. Bilge pumps are centrifugal pumps and nothing will stop the water from flowing through them. If a lot of water is in the bilge and the through hull is below the waterline but higher than the pump a constant pumping and syphoning will occur until the battery dies and then the syphoning will continue until an equilibrium is reached

Putting a loop in the line will help but will not stop syphoning, it will only work if the bilge pump can put a large enough air bubble in the line to break the syphon, something that bilge pumps are not designed to do.

A better solution is to put another through hull well above the water line and cap off the through hull below the water line or use it for an intake for something.