From:
http://www.fleshlight.com/faq-general/
What is the best way to clean the Fleshlight?
Simply rinse your removeable Fleshlight sleeve with warm water from your sink and allow time for it to dry before storing. Do NOT use soap to clean your Real Feel Superskin sleeve. For tough cleaning, we suggest using a little isopropyl alcohol. To maintain that soft feel, sprinkle a liberal amount of corn starch on the sleeve and shake off the excess powder. We do NOT recommend the use of talcum or baby powder. NOTE: Powdering an Ice Fleshlight masturbation sleeve with anything other than corn starch will cause it to cloud over and lose its clear quality.