I have both plastic and metal 6 gallon portable boat fuel tanks with no manual vent. What a pain in the rear!...especially on a hot day when the plastic ones swell up. They both can have vapor lock issues while the engine is running if the fuel cap is fully tightened but will leak fuel due to splashing if the caps are loose. Is it possible to drill a tiny hole in the cap to provide a vent? Does anybody have a home-grown fix that works? Thanks in advance for any and all ideas. Happy Boating! :joyous: