I always have a small amount of water in the bilge, less than 1/2 inch. It seems the bilge pump and float switch are working properly. If I manually turn on the pump most of the water in the bilge is vacuumed up but when I release the manual switch the water comes back in via the pump. Is there something I am missing? Shouldn't there be some type of check valve that would prevent the water from flowing back into the bilge? Your advice is appreciated.