Just checking out new boards and thought I'd comment on this one.
I don't know how well it will work on tall
decanters of small diameters, but works great for cleaning glass coffee pots. You just add a little
water, throw in a bunch of ice cubes and swirl around for a couple of minutes. If you have some really tough stains you add a couple of tablespoons of salt and its acts like a scrubber but won't scratch the glass.