Why not a mechanical repair. Drill a hole through the leak and install a fastener such as a bolt with plastic washers for sealing. If you can only access one side there are pop rivets with closed ends that wouldn't leak. A well nut might also work (need some permatex to seal the bolt). Advantage is that the galvanizing around the repair will be saved (and the only machinery you need is a drill).
Bill

I have resorted to the "screw w/ rubber washer" as Bill suggested on cold water storage tanks before. It held up for many years before I switched over to County water. The well water was extremely hard on hot water heaters and cold water storage tanks, so we switched.
John Wright

I have to also agree with the above replys, but have encountered these "pin holes" on quite a few water tanks and irrigation systems made of galvanized as well as the tanks with an inner coat of some kind of glassy material found on hot water heaters too, not to mention air compressors and other tanks. Hopefully, they are actually nothing more than pin holes and therefore not what I usually run into, which are layers of rust which are somehow held together well enough to simulate only a pin hole leak (usually these are around welds made prior to painting and tank completion). Problem is, when you take a wire wheel or brush to the spot, the rust starts flaking off rather easily, and you end up with a hole 2 inches in diameter with metal surrounding it that is about as thin as a piece of paper. Hope this isn't your case, but if it is, I know of several ways to repair successfully and just holler if you are curious.

Hope that helps!
G. L.

Having a "few pin holes" could mean you have a internal corrosion problem. Which means the wall thickness of the tank could be very thin. I like the rubber washer gasket repair. Just keep in mind it may be temporary. Any weld repair you try to make might result in a larger hole and you'll end up patching anyways.

Good luck.

Mike