Put them in your washing machine with about a dozen old face cloths, add powder as normal and wash on a warm wash only. Fill the drum about 1/2 full with balls, you will need to cut a piece of card in a half moon shape to hold them in and slide it out as you close the door. Stand them on a towel afterwards with the hole at the bottom and let gravity and the suction from the towel empty them, if they will not drain, pierce another tiny hole oppisite the original, this will let air in and the water out.
Have fun......