[CHANMADD]

If the gas tank is perfectly sealed........when the fuel pump sucks the gas out of the tank.....it will eventually cause a vacuum in the tank creating more suction back into the tank than the pump can overcome.........So as the fuel goes out , air lust be allowed into the tank to replace the space the fuel took....some gas caps have a small breather hole , and others have a remote mounted breather.....or an in tank breather ......these breathers should be of the type that has a tipover valve that stops the flow of fuel out the breather if overfilled or if the car has a rollover accident......so you should have a breather with a tipover valve......