UNTIL NOW!! I finally found the perfect tools for cleaning any water bottle.
So these are both pretty simple bristle brushes but they had just not occurred to me to use! I was sooo close to throwing out about 6 water bottles that had grime that the dish washer couldn't handle. I had tried soaking them and scrubbing them but my hands were getting cut up trying to reach the sponge to get to the nasty black mildew.
I finally found the Libman brush in the cleaning isle at the grocery store and then got the even better Munchkin brand scrubber. It is made for baby bottles so it really works perfectly to get to the bottom of the bottle where it is all curved and impossible to clean.
So don't throw those bottles away just yet! The mildew can be conquered. Maybe everyone has already figured this out but I was super psyched when I discovered these guys a little while ago.