One line goes from the clunk to the pump then the carb.
Another line is the over flow line. Also used as the vent line. It goes to the front top part of the tank inside
Third line is the fill line and should go to bottom front part of the tank inside. After filling you will have to plug this line or the fuel will run out. Also you can use this line to drain the tank by tilting the plane nose down.
With the plane right side up no fuel will run out the vent line. When the engine is running The pump sucks fuel from the tank and air is sucked in the vent line so no fuel will run out when the plane is inverted. Hope this answers you question.