Depends on how old the tank is. But on any of them, it could be the o-ring in the fuel hose connector. Replace the o-ring or the entire connector.
The older tanks have two small pins that get pushed in when you push the fuel connector on. Look at those two small pins and you will see a brass washer surrounding one of them. Behind that washer is a tiny o-ring. If the o-ring is worn, it will slop gas out and suck air. It is repaired by removing the core plugs on the opposite side of the housing, removing the pins, then pry the brass washer out. Replace the o-ring, stake the washer back in, and re-assemble with new core plugs. There are two sizes of those tiny o-rings, according to year built. You will need to know which ones to order. Or order both to be safe.