Put enough air in it and it may push the floor of the tank down and both sides out at the same time, I've seen it happen several times.Air compressor line into the filler hole with a rag around it to seal it, and petcock turned off. It May or may not do something. Depends on just how bad the dent is, if it has alot of creases to it then it likely won't pop out. Have to weld rods on it to pull out with slide hammer. Or just hunt down another tank if you don't like body work.