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An important caveat that I found missing from the above:

This will almost certainly damage your wireless keyboard. This may be common sense to most, but it bears pointing out just for sake of completeness. Keyboards that have those extra "quick launch" keys also may suffer damage as a result of beig "dishwashed". For those of us who have a normal, sane, "vanilla" keyboard, this method works like a charm (I've seen 5 different keyboards go through a grand total of roughly 50 wash cycles, with no ill effect).

If putting your keyboard in the washing machine dosen't correct your problem, consider removing all of the keys first, and washing them seperately in a bowl while you put the rest of the keyboard in the washing machine. Yes, gunk this bad exists.