These should eliminate the bubbles getting into the fuel line if it is a foaming issue, but won't solve why its making the bubbles.

http://www3.towerhobbies.com/cgi-bin...&I=LXXF25&P=ML <- Too expensive

http://www3.towerhobbies.com/cgi-bin...?&I=LXD741&P=0 <- Just right

You need to pad the tank with foam because it is vibrating with the engine causing the bubbles.

Another way to have bubbles, is that you have a pressure leak and the fuel line is drawing air into itself through a hole, tear, or loose connection.