Did you know that bleach dissolves hair? It's true! This is due to the chemical make up of the two. Bleach is a "basic" chemical and hair is "acidic". The neutralization reaction between an acid and a base produces a salt and water. Bleach can dissolve any fiber that has acidic properties.
Next time you have a bathroom sink, shower, or bathtub draining slow try pouring a cup of liquid bleach into the drain. Be sure to rinse off any metal finishes with a little bit of water so they wont get damaged. After about a half hour any hair the bleach is in contact with will dissolve. If it doesn't get rid of the stoppage completely then try another application of a cup of bleach.
This may not always work. There are many other things that can clog a drain line... floss, food, soap scum, hard water, GI JOE's, etc... If the bleach doesn't work give me a call. I'm always happy to come fix your drain. But hopefully the bleach tip will save you a few calls.
Liquid bleach is much less expensive than bottled drain cleaners... and for hair stoppages it's much more effective (which usually bathroom sinks, showers and tubs are hair stoppages).
Caution: Of course you should always wear protective clothing, gloves, and goggles when handling chemicals such as bleach. Please be cautious!
(Edit: If your drain is completely stopped and is not draining at all it is best to call a plumber. Any chemical, if left to sit in a pipe, if it is unable to clear out the stoppage it has the potential to cause further problems. Bleach is less likely to cause any problems when compared to other chemical "drain cleaners". But if the drain isn't draining at all then the bleach, or any other chemical, will not be able to get down the drain to the problem area.)