is there a vent on the gas tank? I'm sure there is but I have no clue where it would be.[/QUOTE
if said tank has only a single fuel line & no other fittings then it must have a vented cap
if it has two fuel lines AKA supply & return then in can use a vented cap but most prob has some kind of vac vent system.
to help in locating vent need the following .
?#1 what kinda gas tank
?#2 is it on a vehicle or some kind of equipment
?#3 what is the appx age of #1 or #2