Originally Posted by The10mmKid
I get my 20# refilled at the local Equipment Rental place for $20
They fill it until the vent spews liquid.
Not such a good idea. Some surface area on top of the liquid propane is necessary for evaporation. You can starve a flame when the tank is overfilled. Also, a completely full tank will vent as it warms up, not a good idea in a car. That's the reason why new tanks have an overfill prevention device.