Physically Impossible

I fully agree with the statement," gas cannot be sucked out of the carburetor bowls". But still the gas can be sucked back into the tank, leaving the fuel lines and pump dry. When the gas tank cools down their is a bit of a vacuum that takes place, especially when the gas tank vent cap is not working or if some of the emission vacuum lines are plugged and or removed. I installed a check valve in the fuel line just to stop this sort of thing....