I have a 1978 21 Hydrasports CC with a built in 60 gallon fuel tank. Can't get the ball to pump gas from the tank. Can blow back into tank and here it bubble (may be a little bit restricted). I am getting ready to poke the syphon tube good and replace the gas line. Maybe there is a small crack in the line? A while back I bypassed the valve that said full /half /off at the tank. Has two down tubes into tank. Is one to bottom and one only 1/2 way down? If so, I must be using the one to the bottom now. Any ideas about this?