You should be pumping the fuel out using the line going to the carb. If you can't pump the fuel and your engine will only run on a prime then you either have a tear in the fuel pick up line in the tankagainst the nipple or your clunk has been thrown foward and is up against the top of the tank. My guess is the clunk is wedged forward in the tank.Shake the plane a little and see if you can hear the clunk tapping in the tank. If you do then you probably have a hole in the fuel line and will need to remove the tank and put in a new pick up line. Sometimes if the clunk is stuck a good shake will free it up.