As mentioned, it is a check valve. Lets air in so you can suck fuel out, but won't let any vapors from expansion escape.
Those tanks can build enough pressure to blow the needle off of the seat in a carbureted engine. Best to vent them somehow.
so its like a fart . a quiet sneaky slipping out one was just fine and not terribly embarrassing back when.
and the government decided to stop that and make it one of them omg farts instead ....
they always come up with some sort of ding dong plan .....regulating tank farts ....just lovely....
so what do you do ,,,,I work for the government , our dept regulates fart pressure ,,,,
sum kawl me tha outlaw ketchn whalesCentral Minn LIKED above postS10CHEVY, wannabe fisherman haha