put keycaps in a basin, pop in 2 or 3 denture tabs, depending on amount of keycaps and how dirty it is or how much of a clean freak you are.
usually i pop in 2. fill up the basin with water (luke warm or slight warm water is recommended) just enough to cover up the keycaps, you don't want to dilute the denture tabs too much. leave it for 30 minutes or more, or it depends on your dota game or drama series, whichever applies.
rinse with clean water, dry it, make sure it's all dried up before putting back on your keyboard.