Galvanised water tanks are relatively sturdy and cheap, making them useful for such applications as watering livestock and storing large amounts of water. The tanks are covered in a coating of zinc, which protects the underlying metal from rust and corrosion. Over time, though, galvanised tanks can still develop leaks. Rather than discarding a leaking galvanised tank, fix small holes easily and inexpensively using simple tools and items from the hardware store.
Hammer flat any sharp edges which are protruding into the inside of the tank around the leaking hole.
Place a small block of wood adjacent to the pinhole leak on the outside of the tank. Scraps from two-by-fours work fine.
Hammer a 4cm (1 1/2-inch) threaded roofing nail with a rubber washer through the pinhole leak, from the inside of the tank. Drive the nail into the block of wood until the rubber washer on the nail is tightly seated against the metal of the tank, plugging the leak.
Drain the tank below the level of the leak.
Drill the leaking hole to make it smooth and regular. Use a drill bit at least 1cm (3/8-inch) in diameter.
Insert a boiler repair plug into the hole. The toggle bar should be on the inside of the tank and the rubber washer, on the outside. Once in place, the toggle bar will spring back into an open position, securing the plug in place.
Tighten the nut on the boiler repair plug until the rubber washer is tightly seated, sealing the leak.
For larger leaks in open galvanised stock tanks, either a boiler repair plug or a nut and bolt with two rubber washers and two metal washers can be used.
If a heavy water tank must be moved or lifted to repair a leak, have one or more helpers hold it securely to prevent possible injury from a falling or rolling tank.