1989 fuel tank vent prob

My fuel tank is about 1.5 yrs old. I just replaced the fuel tak cap after it seemed like everytime i went to put gas in the tank was under immense pressure. This still didnt solve the problem and the pressue actually made the tank get a hairline crack that would only leak with the great pressure but once the cap was removed it was ok. My question is the breather line that comes outta this car, can i clear this without riping this car apart and would this be the problem or could it be something else, thanks for any advice