The best way to clean an onahole is to wipe it out with tissues several times, until dry, then store. As long as the toy is fully dried inside you should have no issues. It is sometimes possible to turn onaholes inside out to clean, though we generally don't recommend this as it could make the onahole tear, or otherwise shorten the life of the onahole.
For a more in-depth guide, click this
link.
