Ice is the secret
A great, and inexpensive way to get rid of old wine stains in wine decanters is chop up ice so it can fit down the neck of your decanter, add a little water and swirl. Stains quickly disappear. The water will start to turn color, as the ice scrapes the wine stains off the sides of the decanter.
Its that simple. Try it. You'll be amazed by this simple solution.