Do you have a decanter that has a stain making the glass seem dull or diluted?  Well, if this is your decanter then you may need to clean it to remove the stain.  Cleaning a decanter is not as easy as taking a cloth and just wiping the inside of the bottle.  Most likely the bottle top will not allow enough room for you to put your hand inside.  In this case you will have to use another means of cleaning you decanter.  There are a number of ways to clean decanters and if you look on the net you will find accounts from people that swear by their method.  Some are simple, some are dangerous and may be poisonous and some may just take a trip to the grocery store to get a few requirements.  Below, I will outline a few simple ways to clean your decanter.

The simplest way that I have found to clean a decanter is to use ice.  Yes, I mean ice from your refrigerator or ice box.  The ice needs to be in block size but small enough to fit through the hole in your decanter.  If your ice cubes are too big to fit but break them into smaller piece but not too small or they just will not do the job.  Put the ice cubes inside the decanter and add a small amount of water.  Next take your hand and spin the decanter in a circle making the ice cubes scrape the sides of the decanter, the scraping with cut through the stain on your decanter after a while removing and cleaning the crystal glass.  Once the stain has been removed use soap and water to finish the final rinse.  This is a simple way to clean your decanter and is not toxic in any way.  Also, if the ice milts before you are able to get all the stains off of the sides of the crystal decanter then just add more ice.

An even more simple solution to cleaning your decanter come from using a denture cleaning tablet.  That is right; I said a denture cleaning table.  Dentures need to be clean nightly so it is important to have a solution that the denture can soak in that will remove food and stains caused by food and drinks.  That being said it is perfect for cleaning a wine decanter and it will leave it odorless and remove any lingering taste from previous wine decanting sessions.  So here are the instructions.  First, go to your local pharmacy and purchase a denture cleaning tablet system.  Anyone will do. They all do just about the same thing.  Second take your decanter out and place a tablet inside of the decanter.  Next, add water to the decanter.  You will see a reaction from the denture cleaning tablet.  This is normal as it releases its solution.  Close up the decanter if you have a top for it.  If you don't that is ok.  Just leave it open for the night.  In the morning rinse it with distilled water and you are done.  You will have an odorless, stainless, wine decanter ready for your next wine.
source: here