If I'm reading your post correctly, I think you're doing it backwards... disconnect the supply line from the tank where it enters the needle valve. This where the fuel goes in. Disconnect the pressure line from the tap on the muffler. Connect your fuel pump to the supply line from the tank, point the pressure line from the muffler in a safe direction and start pumping... when fuel comes out the muffler line, the tank is full. Some people will even connect a small fuel tank to the muffler line to catch any overflow