OS makes a "bubbleless clunk" that works pretty good. It should.. they want $15.99 for the darned thing. (the first one, the one on the left)
http://www3.towerhobbies.com/cgi-bin...&I=LXXF25&P=ML
Dubro also makes a fuel filter that works just like the OS one for a heck of a lot less.. Tower has it for $2.49 (the second one, the one on the right)
http://www3.towerhobbies.com/cgi-bin...&I=LXD741&P=SM
I bought several of the Dubro ones and use them on all my planes. I never had bubble problems, so I can't say if they work or not, but, as I said, I don't have any fuel line bubbles at all.
CGr.