Diamond stones are your workhorses for getting a knife sharp. They can also get really, really grimy. The best method for keeping your diamond stones clean is to wash them with warm, soapy water and let them air dry. Any household dish soap is acceptable and if your stones seem like they need more than just a soak, an old toothbrush works well to clean grit out of the nooks and crannies. Stand your stones on end on a paper towel to allow water to drain from the handles while they air dry.