A Single Running Toilet Can Increase Your Water Bill By 50%

For a toilet that keeps refilling, you need to replace the gasket on the flush valve.

It can be a flap or a round gasket. You need to know the style and the size. You have 2 sizes, a 2 inch and a 3 inch flush valve.

Replacing the gasket will stop the toilet from running.

Now here's another fix that fairly rare.

If you have a leak between the tank and toilet bowl (water on the floor below the tank). Here's what you need to replace.