Life is all about the details, but sometimes, those details aren’t pleasant. If your toilet is running, you’re potentially wasting gallons of water a day. But don’t despair! Most often, it’s just a simple fix, no tools — or plumber — required. The first thing to understand is that toilets work on gravity. When you push down the lever it lifts up a rubber flapper, allowing water to run out of the tank and into the bowl.