With the air-pressure method you run the risk of deforming the shape of the gas tank. It can force out all the shaped recesses if there's too much pressure.
A friend of mine had decent success with one of those kits you see on TV - that involve some hot glue, a suction cup, and a screw-type device that will allow you to pull a dent outward. I think he got the kit for $30 or so. You may be able to find it at an autoparts store.
Otherwise, a professional will probably be your best bet if you want it looking like new again.
Those kits from TV are only good on shallow dents that dont involve a crease or body line.
Some tanks have a fuel pump that mounts to the bottom that when removed has a nice big hole that a body spoon or hammer will fit in nicely. Can remove the dent that way, but probably will need to be repainted in that area.
Don't try to remove the dent with air pressure. I did that(carefully) and destroyed an SV tank. Damn shame too cause it was one I'd gotten off ebay and the dent only needed be filled with reinforced fiberglass filler and sanded and woulda been fine. Instead... I had to be smart about it.
I devised fittings to seal the tank top and bottom. Top fitting had an air spigot. I put the tank down on some pillows that took up the space underneath. My idea here being to eliminate the possibility of the inside being forced out by the air psi. I put all my weight on the top of the tank and applied the pressure. At first the dent(tank side as usual) came out somewhat. Figured I could get it a bit more. Thats when the bottom of the tank popped right outward making some horrible kinks in the concave metal underneath.
Turned out the bottom pushed out so far I can't even get it on the bike any longer. Grrrrrrrrrrr.
There are body shop guys who can weld pull rods on the dent and pull it out/rework it. Go that route or buy a used one on ebay.
A forum community dedicated to all motorcycle owners and enthusiasts. Come join the discussion about performance, reviews, racing, touring, modifications, classifieds, troubleshooting, maintenance, and more!