Vinegar is one of my favorite cleaners. Also works well cleaning dirty stuck on dishes and pots & pans. I have this vinegar book, there are tons and tons of ways to use it and make your life simple.
Anyone with hard water in their community can relate to the problem of some pretty impregnable stains. I used to scrub fruitlessly at toilet bowl rings until one day I tried pouring in some white vinegar (maybe a cup or two) and leaving it overnight. Everything came off in about a minute after that. The tip goes on to add that if you’re in a hurry, you can leave the vinegar in there for as little as twenty minutes; I’ve gotten this to work on showers and sinks as well.