Remember when you were little and you (or a class mate) did a science project where a volcano is created from normal homemade science? Imagine what that simple little chemistry experiment can do in areas of your home!
If you have a clog in your drain, or its simply just dirty in there try the following.
Baking Soda or Borax
Take about half a cup of baking soda and about a tablespoon of normal table salt (it doesnt matter if its iodized or not) and pour it down your drain. Make sure it gets in there - in case its clogged and water is backing up just make sure it settles or gets as far in there as you can. It may actually help to try and plunge the drain first to make sure you can get it down there.
Next pour about half a cup of vinegar down after it.
Now enjoy the fizzy fun!
After the fizzing stops if no water has gone down or you aren't satisfied with the results pour a little extra vinegar down there. Now this time when the fizzy fun stops run the hot water down the drain.
Everything should be broken up and your drain should be sparkling inside! Congrats, you just saved about 10 bucks by doing it yourself instead of buying Drain-o!