Using air to remove a dent from a motorcycle gas tank is one of the easiest ways to achieve the results without drilling holes for a conventional dent removal tool. This process is not widely practiced since the invention of the new pin setters allowing the removal of dents without drilling.
Begin by emptying and removing the tank from the framework of the cycle. Don't attempt to do this with the tank installed.
Rinse the tank repeatedly to remove any gasoline residue allow it to dry or blow it dry with compressed air.
Remove all lines and fittings from the tank, replace them with the proper sized plugs and or caps.
Leave one of the larger fittings unplugged this is where you will attach your air line.
Using a proper sized fitting for the particular tank you have on hand, attach the air line and begin to pressurize the tank. Don't pressurize the tank beyond 125 PSI.
As the tank is being pressurized begin to heat the center of the dent constantly moving the torch in an outward circular motion heat and re-heat the dented area in the steel, slight taps around the circumference of the non-heated edges of the dent will help to speed the process.
The dent will come out as the metal is heated and approaching a cherry red color. Try not to let the red area become larger than the dent, you could create a bubble in the metal.
Allow the area to cool slightly then chill the spot with a damp rag.
Finish with body filler and glaze as you would any other body work. Prime the area, sand the repair and a few inches beyond with fine sand paper(400 grit) . It is always best to use a sealer before you paint but it is not required.