Why do drains clog? The short answer is because of the way we use them. Obviously, even though it's not supposed to happen, water isn't the only thing going down most drains. In fact, knowing what has clogged your drain can be an important step in knowing how to clear the clog. At the kitchen sink, grease and small particles of food can make their way into the drain. In the bathroom, hair and soap scum are the biggest offenders. Over time, these substances can build up and begin to line the drain, and then one day, another piece of food or another clump of hair is all it takes to block the drain [source: Goodway].
Foreign objects, such as jewelry, bottle tops or toys, can also fall into a drain and clog it. If that's the case, drain cleaners won't help unblock the drain. You'll need to remove the object or call a plumber to do it for you.
Assuming your problem isn't a foreign object, first try to locate the clog. Start by removing, checking and cleaning the stopper or strainer at the entrance to the drain. Some strainers are easily removed by hand, but others may require a screwdriver or pliers. Remove anything you can reach and then try pouring hot water down the drain.
The next step is to try using a plunger on the drain, and if that doesn't work, try removing and cleaning the sink's trap. After that, you may want to try a sewer snake, or auger. If none of these efforts works, it's time to use a drain-cleaning product [source: Harrison]. Read on to learn the pros and cons of various drain cleaners.