How to Fix a Running Toilet in 15 Minutes

A toilet that won't stop running wastes hundreds of gallons a week. The fix is usually a $12 part and a single trip to the hardware store.

Lift the lid off the tank and watch what happens after a flush. Nine times out of ten, either the flapper isn't sealing, or the fill valve runs past the shutoff line and trickles into the overflow tube.

Test the flapper first. Drop a few drops of food coloring in the tank, wait 15 minutes without flushing, and check the bowl. Colored water in the bowl means the flapper is leaking — a $5 universal flapper from any hardware store solves it. Shut the water off at the angle stop, flush to drain the tank, swap the flapper, done.

If the flapper is fine, the fill valve is the culprit. Bend the float arm down (older ballcock style) or slide the float clip lower on a modern Fluidmaster so the water shuts off about an inch below the top of the overflow tube. If the valve still hisses, replace the whole assembly — it's $12 and takes 10 minutes.

Either repair pays for itself in a single billing cycle. A silently running toilet in a Bellevue home I diagnosed last month was adding $40/month to the water bill.