Can't put gas in tank?

Vent hole plugged, fuel pump sucked the tank flat?

I never let the tank get to empty, where is the vent hole? Thanks for the help.

I have no idea where the vent hole is. They used to be in the gas cap in pre-smog days.

With a sealed fuel system, you don't have to let it get empty to flatten the tank, IN THEORY. For every gallon of gas the engine burns, a gallon of air has to get in. If it doesn't, something's got to give. With a really strong tank and fuel pump, you'll just get a vacuum on top of the fuel. But in the real world, either the tank collapses or the fuel pump can't draw. Note: this is all theory. Back in the pre smog days, I heard tales of this, but never very first hand, so I don't know if it really happened.

If you are very patient, how much gas can you get in the tank? How much gas does owner's manual say it should take?