To keep your pumice stone clean, rinse it under warm water after each use to remove any loose skin flakes. Next, wet an old toothbrush with a mixture of warm water and liquid dish soap and brush it all over the stone. Rinse it in warm water again to remove any dirt and other residues. Since bacteria and fungus are common on the feet, it’s a good idea to periodically boil your pumice stone in a pot of water for five minutes to kill any germs. Make sure the stone is completely dry before you store it.