Are you asking about an after market pump like a Perry pump or are you asking about an OS with a built in pump. I have both but i am confused with your question. On my OS 91 with a built in pump, one fuel line comes from the 1st clunk in the fuel tank to the pump. Another line comes from the 2nd fuel tank clunk to my fuel/unfuel line that I leave plugged and a third line comes from the fuel tank vent and vents to the atmosphere, unpluged.