If you fill the tank completely does it still act this way?
I'm still suspecting fuel line or a seal somewhere if you have now fixed the clunk position. The motor does not ever "pull" fuel, it is pushed from the exhaust pressure with a good seal. If it does it when the tank is full, the problem should not be with a hole in the fuel line inside the tank. Pull the fuel line off the motor nipple, pull open the tank lid, and blow into the fuel line. Are the only bubbles coming from the clunk, or is there a hole in the line somewhere inside the tank or anything?