Like he said, bubbles are bad.

I've used the "sintered" brass dubro clunks to great effect to cut down bubbling on the fuel lines.

Remember though that in a nose down attitude with less that 1/2 of a tank, it becomes almost impossible to avoid bubbles as the fuel depletes.

Since the clunk is not permitted to "travel with the fuel" most planes have a tendancy of deadsticking on nose down aerobatics as the tank runs below 1/2.