To know when the tank is full just watch the line going to the vent on the tank. This is the line going to the muffler, when the tank is full, the gas will start coming out of this line. On my Hangar 9 Corsair, I just look through the cowling and the gas will come out of the line. If I am not paying attention the gas will also come out of the muffler but I tr not to have this happen. Good luck.

Tom