The info I have from a site says:
Mix at 10 mg/liter of water for a 10-minute soak, or use “Clear Water” from Jungle Products according to directions. Will kill bacteria and pathogens. Buy potassium permanganate from retail chemical supply stores, or get some from your local school lab.
You could also order it at a pharmacy. I have not used it myself, only because it will stain your skin (wear rubber gloves) and I am.... um.... clutsy.... so I don't trust myself with it.