I have found some older threads on this topic including installation of check valve inside the wing root (Tim Olson) or inside cabin (Vic Syracuse). There is also the idea of mounting a rudder cable fairlead over the vent on the outside of the wing (Vic Syracuse). Another is drilling a small hole in the tubing inside the wing root (simplest). Is there any consensus, or even a better idea about this problem? I don't find anything recent, so maybe it is a settled issue.