A "running" toilet is annoying. There's that relentless hissing or near constant flushing sound as it continually tries to fill the tank. But it's also expensive and wasteful. Your average running toilet can flush away two gallons of water per minute. And a slow, silent leak in your toilet can waste up to 7,000 gallons of water per month. The good news is that often, it's a simple fix. No plumber—or even tools—required. And nothing offers a surge of testosterone quite like fixing something around the house. But to fix your throne, you've got to know how it works. Toilets work on gravity. When you push down the lever, a chain pulls up a rubber flapper at the bottom of the tank, allowing water to run out and into the bowl below. When the water in the tank runs out, the flapper closes and the tank starts refilling. The water rises until a float closes the intake. Pretty simple, but any one of those things could be your culprit. Here are three common causes of a running toilet and how to fix them.