Your corset should never be washed. If your corset does become wet, you must make sure that it is dried as soon as possible, without damaging the corset, in order to prevent the steel spring boning from rusting. If you have been unable to prevent the steel spring boning from rusting, rust spots should be cleaned with a fabric safe rust remover.
Never dry a wet corset over a metal hanger or other metal object. Never wash or dry your corset in a machine.