Even a small pinhole in your stainless steel sink will cause a major leak, damaging the items housed underneath and leading to potential mold growth. Welding provides a permanent repair, but isn't always an option for do-it-yourselfer's, considering the expertise and equipment required. Another option is stainless steel epoxy, which is applied without the need for specialized equipment and provides a strong, waterproof seal.
Sand the surface surrounding the hole with fine-grit sandpaper to roughen up the stainless steel, which allows the repair products to adhere more effectively. Wipe away the sanding dust with a tack cloth.
Wipe down the surface surrounding the pinhole on the lower and upper sink surfaces with a commercial kitchen cleaner and a nylon scrub brush. This removes any impurities, dirt and debris that prevent the epoxy from adhering effectively.
Combine the stainless steel epoxy according to the label's directions. Slip on a pair of rubber gloves, climb under the stainless steel sink and apply the epoxy to the pinhole with your gloved hand. Work the epoxy into the pinhole until it is completely filled.
Examine the sink's upper surface for any epoxy that oozed through the hole. Wipe away any excess epoxy immediately with a damp cloth.
Allow the epoxy to cure according to the package directions. Run a trickle of water into the sink and check the fix for any remaining leaks. If the sink is still leaking, apply another coat of the epoxy in the same manner as above.