Do you fill it to the full gauge or when it begins to overflow. My newest unit seems to get water in the vent tube and it fools you into thinking that it is full when you are filling when it is actually blowing back out the fill hole due to pressure building up in the tank. The only way I can correct this is to stuff a rag in the fill hole around the hose until the pressure blows to water out the vent in a big woosh. Be careful that your tank isn't really full or it could rupture the tank. It would be nice to have a second gauge at the fill port.