I have a dual tank on my BAe (and just like gadix said). your top tank leave as is, just take the tube that was to your engine and run that end into 2nd tank. That will fill it as the fuel is used from the 2nd tank. leave the muffler line to the muffler.....now on the 2nd tank run one line to the engine and the other will be your fill line.Now when you fill your bird the 2nd tank will fill then the (top) 1st tank.
Tuskegee
U.S.Army(ret.)