I usually just clean them in the kitchen sink. I clean them as they need to be cleaned, I don't really have a schedule. Some snakes are dirtier than others... i.e. - tipping over water bowls, urinating more frequently, etc.

As goes for water.... I replace the water everyday. If you use a water conditioner then you need to clean them everyday otherwise you will get build up in them because there is nothing in the water to prevent fungus and bacteria build up. I don't use conditioner anymore, so I just replace the water everyday, and then clean the dishes at the end of the week.