Amuller is correct. One pin lets air in while running, while the other allows fuel to be pulled from the tank, when the line fitting is attached thereby pushing the pins in. If the o-ring on the fuel outlet is worn, it can empty the tank in hot weather, if allowed. Doesn’t have to be in direct sun, but that sure accelerates the issue. It will get up to 110 F this week, at my house. Because I replaced the o-rings for the pins, the tanks did not leak when stored, even when hot. By not replacing the quad ring, as soon as the fuel inlet pin was pushed in, the leakage began.
I really hope this solves the issue. It should; makes complete sense.
I very much appreciate the help and knowledge.
Stay cool, y’all.
Alan