Oxalic acid is also called wood bleach, and it is available at most home repair stores. If you have difficult rust stains on chrome, other metals and just about anywhere, you can remove them using oxalic acid. Just remember, oxalic acid is extremely toxic and can make you very ill if ingested. Be sure to wear protective gloves when using it, wash your hands when you are done, and keep this cleaning product out of reach of children.
Wipe down the item in question. Rust removal is easier if there is not additional dirt and grime in the way of the cleaning solutions.
Dilute the oxalic acid in the tub. This will just involve adding water, but different concentrations require different amounts of water, so refer to the specific dilution instructions on the container. Some come pre-mixed and can be poured directly in the tub. You should be wearing your gloves at this time.
Place the rusted items in the tub. They can soak for 12 to 36 hours. Monitor their progress by removing them periodically and wiping them down with a clean, non-abrasive cloth or scrubbing pad.
Target stubborn rust spots with a toothbrush. You can dip the toothbrush in the oxalic acid and then scrub the remaining rust spots. This will remove any "sticky" rust that is not dissolving in the mixture.
Rinse off your newly clean metal. Run clean water over the metal to get all traces of the acid off.
Dry the metal thoroughly. Use a clean, soft cloth. Make sure there is no remaining moisture or you may have to repeat the entire process later.
Look for oxalic acid in laundry detergents if you need to get rust stains out of clothing.
Always wear protective gloves when working with oxalic acid.