We learned this one from a plumber. He told us that for a clogged drain, rather than spending $$$ on Liquid Drano & the like, there is a cheaper, easier way. All you need to do is poor bleach into your clogged sink (the amount you pour depends on how stubborn the clog is, generally use about 6-8 cups worth) then follow this with a pot of near boiling to boiling pot of water. Repeat as necessary.
We were also told that to keep drains clean, odor free, and prevent future clogging, to do this about once every 6 months. I recently had a bad clog in our bathroom sink & this worked after only 2 "doses" of bleach & boiling water. I like the idea of doing this as opposed to using something full of who know what kind of nasty chemicals!!