Rust stains in sinks are usually the byproduct of hard water or bacteria build-up in the hot water tank. The stains appear to be seemingly permanent, but they aren't. Here's a simple way to remove rust stains from your sink.
Rub toothpaste onto the stain. Be sure to cover it entirely.
Sprinkle baking soda over the toothpaste and allow it to sit for several minutes.
Using a nonabrasive clean cloth, rub the toothpaste and baking soda into the stain until it is gone. Repeat as needed.
Apply lighter fluid to a non-abrasive cloth and rub it on the stain. For safety reasons, use gloves and keep away from open flames. Scrub until the rust is completely gone. Remove and immediately wash any cloth material that came in contact with the lighter fluid as it is highly flammable.
Pour club soda or vinegar onto a new non-abrasive cloth and wipe the area clean of any residual spots and streaks.
Use a clean dry non-abrasive cloth to dry the sink.
Pour hydrogen peroxide onto the stain.
Sprinkle cream of tartar onto the hydrogen peroxide and allow it to sit for 30 minutes.
Wipe the area clean with a soft clean cloth and rinse well.
In addition to home remedies there are many products available on the market for rust removal. Red-B-Gone, Whink, Bar Keepers Friend, and Iron Out are a few popular choices.
Stainless steel sinks scratch easily, so do not use anything abrasive to clean them.