To see where the pin hole is, shine a flashlight underneath the sink and look from above and you will instantly see the small pin hole of light.
rough up the underside of the sink where the pin hole is with 200 to 400-grit sandpaper to remove contaminates from the surface. Wipe the surface with a clean damp cloth to remove the dust from the sanding and then wipe dry with a clean dry micro towel. Buy some stainless steel epoxy and mix according to instructions. Apply the epoxy to the bottom of the sink where the puncture is. Work the epoxy into the hole and surrounding area. Allow the epoxy to cure according to instructions before using the sink. lightly sand any epoxy that has entered the inside of the sink through the puncture with the sandpaper to finish the repair.
JoeThePlumber
July 2010