Instruct: Classify the given Amazon review into its appropriate rating category
Query: Not easy to clean

I'm on number 2 of 4 (not including the one that originally came with the bottle). Not easy to clean. Even with the camelbak brushes, it's hard to completely clear out the top of the valve, so eventually you will get a build up of backwash and (if you have anything other than water in it) possible mold. While it is dishwasher safe, the design doesn't allow for full cleaning. I'm getting about 3-4 months out of each before I just have to throw it away and pull out a new one.