To *clean* the toy, soap and water is just dandy.
To *sterilize* the toy, you can do three things. a) Boil it in a pot for 3 minutes, b) put it in the dishwasher (top shelf, no soap), or c) wipe it down with a 10% bleach solution.
You only need to sterilize it everyone once in a while, OR if you're sharing it with new people, OR if you or your partner has any type of genital infection (yeast, URI, etc).
Hope that helps!