External Fuel Tank Vent on a 20

[Bushwacker]

Make sure you have a riser loop in the vent line, i.e. make sure the vent line goes ABOVE the vent fitting before it drops down to the fuel tank. It's very difficult to prevent water from getting into the vent fitting when a wave hits the side of the boat, but if you have a riser loop several inches above the fitting, that should keep any water that gets into the vent fitting from getting into the tank. Also make sure that the O-ring on the filler cap and the sending unit gasket are't leaking!