Some caps are marketed as "pressure/vacuum" and they vent only when the internal pressure in the tank goes above a certain level, or drops to a preset vacuum. Those don't work well in place of a cap with a simple vent hole. You can thank the tree huggers and their obsession with hydrocarbon vapors for that kind of nonsense!
Jerry
I suppose this the same reasoning behind the modern gas cans that have no vent/ inadequate vent. My 5 gal can takes about 6 hrs to empty. Every time I use it, I say I'm going to drill a hole. But then I hop on the mower and onto the next item and forget.
