I am cleaning the gas tank on a 51 chevy coupe.......I have the tank off the car and am using liquids to dissolve the 'stuff'. My problem is: I can't get any gas to run out of the fuel hook up on the tank, is there a no backflo valve inside the pick up tube or is it plugged....I have blown it out with compressed air but still no luck getting it to flo out......help!!!!!!!! Pat