I always rinse my bottles after pouring and use a cleaner and sanitize before using again. For some reason the last batch I bottled I took a bottle brush, cut off the handle and connected it to a drill. I put some cleaner in the bottle, ran the drill for 5-10 seconds then drained. As I progressed I was amazed at how dirty the cleaning solution was getting. They "looked" clean before I did that, but apparently were not.