Any local hardware store sells a chemical called wood bleach. The real name of the good stuff in it is Oxalic Acid, harmless to plastics and most metals, but it dissolves rust. It was the main ingrediant in Duponts Super 7 Radiator cleaner, the only stuff that ever actually worked. So you can buy just the Oxalic Acid, I do from a local chemical company. One more thing, do a google search for amounts, and use warm water.