On a "normal" tank you have one line that goes to the carb and one line (the pressure or vent line) that goes to the muffler. You fill the tank thru the carb line. If possible, disconnect the "vent" line from the muffler. When you tank is full, you will have fuel come out the vent line. The reason for no "flip" tops is that the fuel tank is normally enclosed inside the fuse. Plus the airplane tank is sealed at the stopper. Cars normally do not have the same duration of different pitch attitudes that planes do. Also, the vent line is normally connected the brass tube that has an upward bend to the top of the fuel tank. The carb line should have a clunk on the end (inside the fuel tank). Do not mix the two lines up, or your engine will die from fuel exhaustion once the fuel can no longer be pulled through the vent line.