A Lucky Accident

I have several Nalgene bottles, the polycarbonate ones, which I use to brew and drink tea. Over a period of weeks, they build up a crust of bacterial growth stained by tea on the inside of the bottle. After much trial and error, I found that soaking the bottles in a saturated solution of baking soda would soften the crust enough to let it be scrubbed off with a brush.
Several classic discoveries were made by accident: Alexander Fleming discovering penicillin; Alexander Graham Bell finding out his telephone worked; etc. Well, while it's not in the same league, you can add me to the list. Forgetting that I wanted to clean a bottle, I put water on to boil. Realizing that heat often speed chemical reactions, I figured I'd use the error to my potential benefit. I spooned baking soda into the bottle and started pouring in the freshly boiled water. It bubbled a bit, but I figured that was just a case of the baking soda reducing the boiling point of the water. I poured more water in and the boiling increased in vigor, boiling over slightly. Since a liter of boiling water is too hot to work with, I left it to cool for about an hour.
When I returned, I took an old toothbrush and put it into the bottle and began to scrub. WOW! The crust just brushed right off, no elbow grease needed! I got out the bigger brush to get the bottom of the bottle. It came off just a easily! Just a couple of minutes work after an hour of waiting - it was a tremendous time saver. So, if you need to remove something like this, boiling water and baking soda may be worth a try.