Rust stains from hot water on appliances can be removed with Zud. Don’t use bleach to clean a hot water rust stain. Sinks and showers with rust stains have leaking occurring. Zud is the best heavy duty cleanser
For starters, do not use chlorine bleach on the rust as it will set an iron stain. When it comes to rust stains in the house, I pull out the oxalic acid. As ominous as oxalic acid sounds, it is a safe household cleaner when used properly. Painters know it as “wood bleach” and use it to remove stains from wood after water damage or paint stripping.
First, I suggest using Zud on your stain. It is a common household cleaner that contains oxalic acid. I have had success removing rust stains from my fiberglass boat by wetting the area and sprinkling Zud on the stain. I kept the area damp and softly worked the Zud back and forth on the stain. Before I knew it the stain was gone.
For a stubborn rust stain, mix a saturated solution of oxalic acid in warm water, one-tablespoon oxalic acid into four ounces water. You should not need much more than that for a small stain. Apply it to the stain three times in ten minutes. Work the area with a soft nylon brush, rinse thoroughly and your stain should be gone.
If the finish of the tub is worn down to bare metal you may have to use appliance touch-up to color the area. If that is the case, use a product called ‘The Must for Rust” on the rusty metal first to kill and seal the rust. This way the rust will not ruin your touch-up paint.
Warning: Follow label warnings and use latex gloves and goggles when undertaking this project.