Carb overflow tube material

I changed to a silicone tube after the plastic one cracked.

Flight Design use poly and Tygon for fuel sight tubes and so do others. I have videos of these tubing that were in fuel contact for 5 years and then removed and bent over against the normal curvature 180 Degrees and never break. For use as just a vent tube that has no full time contact, no pressure or vacuum either tube should be just fine.

https://youtu.be/5E3jSy02pic

My engine is in a RV-12. There is unpredictable airflow inside the cowl in flight. I tested the air pressure at the end of the vent tubes under the bowl bails using the carb balancer hoses. I placed  one hose next to each vent line and ran them into the cockpit and went flying. The pressure reading during flight was many times unequal. This means the carbs are varying rich / lean based on the air pressure above the fuel in the bowl. 

I extended my vent hoses and fitted them into the rear of the air cleaners. The result is smoother running when both carbs are feeding the same mixture.

http://waltsrv12.com/engine/carburetor-vent-line-reposition/