Credit: adavino/Getty Images Knowing how to unclog a drain is helpful when, inevitably, one of your drains isn't flowing as well as it used to. Drains can clog from dirt buildup, soap scum, skin flakes, hair, and other waste. And unclogging a drain is essential for keeping water flowing smoothly and avoiding an overflow. There are plenty of good commercial drain cleaners on the market, even some with plant-based formulas.