Years ago, our local radiator shop did all the gas tank repairs- in our city of 100,000 people. The owner used to take a hose from the exhaust of a nearby idling car, fill the tank with exhaust fumes, and left the car idling the entire time. Now it is just simple chemistry that exhaust gas has almost no oxygen remaining and will not support combustion under any circumstances.
The muffler on our Chevette dropped down, hit the highway, punched a hole in the bottom of the gas tank, all in less then 3 seconds start to finish. I took the car to the shop, they dropped the tank - all but about a gallon of gas had run out through the hole. Bud rolled the tank over, stuck the hose in the filler neck, let it fill for a minute or so and welded it up.
Said he had done it that way all of his life, and it was stupid to drain the last of the gas out and try to dry it out - you might kill yourself. He wanted the tank full of exhaust and did not care about the last gallon of gas. I still stood back a ways!!
Flipped the tank back on, still enough gas to go to the gas station!
Saw Bud out walking the other day, bad knees, 90+ years old.