hi. this is my first post here. i used the search function but didn't find anything.

i have a 92 GMC sierra 1500 5.7L pickup with a lot of miles (230k) on it. anyway, i'm trying to sell it. found a buyer. now, in california, every vehicle needs to be smogged within 90 days of it being sold. i took it to get it smogged: it passed the emmisions, but failed the evap pressure test. i guess they fill the tank with nitrogen and measure the pressure.

where should i begin to look for a leak? i am hoping to sell this truck TOMORROW!!!!!!! please help me!