I take it you are running Nitro as gas gets set up a little different. It can be done 2 different ways 2 fuel lines or 3 lines. Two line 1 goes to the carburator and the clunk in the tank, the second line brass tubing gets turned upwards in the tank and hooks to the muffler, For filling you remove the line to the carburetor and use the muffler for overflow when tank is full.
3 line= 3 brass lines coming out of tank, 1 will go to the clunk connects to carburetor, 1 will be bent up near the top of the tank for overflow when filling tank, will go to the muffler. and 1 will lead to the bottom of the plane for filling and needs to be plugged when running the engine to use muffler pressure to feed the engine.