I gotta interject here. Laughintom did say his tank has surface rust, so I can assume his is a steel tank. The wire wheel and cold galvanizing would be great for that, but I'm worried someone with an aluminum tank would try the same method.
Do NOT use a steel wire brush on an aluminum tank. Traces of the steel wire brush will become imbedded in the surface of the aluminum. This will cause galvanic corrosion, which is caused by placing dissimilar metals together. An electrical current is induced between the steel traces and the aluminum, and will corrode no matter what you paint it with. Same for the cold galvanizing compound. Although next to each other on the galvanic scale, zinc, like steel, will react with the aluminum and eventually cause corrosion, especially in salt water.
(I'm an Inspector on fighter jets. They drilled this into my head years ago)
And Militantmedic,
I've had trouble getting paint to stick to cold galvanizing coated parts. I also build custom cars. I only use CG on hidden undercarriage parts and between welded seams.
It's pretty tough stuff by itself though, and would look good on a tank.
But if you have an aluminum tank that needs refinishing, use only aluminum oxide blast media or paper (no wire brushes or steel wool). Then paint it with epoxy primer and epoxy paint.
Jimlap, you can't powdercoat aluminum? I know how hot powdercoating is, but aluminum doesn't melt before about 1400 deg. (Might weaken it though) But if it won't hurt the tank, it sure seems like it would be the way to go. Very tough stuff.