[Mike C]

We completely rebuilt a '72 Jimmy for my son. Original tank. It was flushed out and looks good inside. Now that the truck is on the road we have found the vent tube going into the tank is plugged. I can put 100psi of air pressure on it and it just blows back out the vent opening. If you hold the rubber nozzle on it tight enough after you stop adding air and let off, it vents pressure back out. So NOTHING goes into the tank.

Anybody had one of these tanks cut apart? Is there some sort of one way valve inside the tank? Trying to push a coat hanger through it forcibly contacts something, and that does not happen in the smaller charcoal cannister fittings. I have an air vacuum pump I may try to hook and and see if it might pop a valve loose.