The general rule is first clean then sanitize. Cleaning gets off all the **** ( that's a highly techncial brewing term) that you can see, sanitizing gets off all the **** you can't see. I have only filled bottles that I personally emptied, so I haven't found a need to clean, I rinse and dry thoroughly after I empty. I saniitize before each bottling session. Once in the dishwasher the night before and once with starsan in a vintator.