They're chlorine-free and environmentally safe! They work on stainless-steel bottles, plastic, glass, porcelain, and silicone. Just put a tablet in with warm water, let fizz for about half an hour, rinse, and admire your freshly clean container.
Promising review: "I wasn't sure if this was a gimmick or not. Turns out it works really well. I have four metal thermos-like containers that are used to keep tea warm every day. Over time, the tea stained the insides and was very difficult to remove. I added one of these tablets to the container, filled it with hot water, and let it sit for a few hours. When I came back to rinse it out, I was literally amazed at how clean it was. I think it looked cleaner than when it was new. I called my wife over to show her, and she was equally impressed. Awesome product!" —Robert A Moreno II
Get 12 tablets from Amazon for $8 (also available in a pack of 32).