I have two Camelbak bottles, one dedicated for water, one for sports drink. I USUALLY rinse out the sports drink bottle with hot water as soon as I get home, Like everyone said, the water-only bottle stays pretty clean. I pull off the valve and take of the ring and clear cap from the lid of the sports drink bottle every few week and clean with hot, soapy water. If I see any black stuff anywhere, I fill the bottle with water and add a dash of bleach and let sit for a few hours. Rinse REALLY well to get all of the bleach out if the bottle.