[header] How to fix a running toilet [title] Turn off the water and drain the toilet. [step] Before you can check the flapper for problems, turn off the water to the toilet. Flush the toilet to drain excess water from the tank. 
This will allow you to inspect the flapper without having the toilet running constantly. [substeps] The flapper is a round rubber seal that stops water from draining from the tank and into the toilet bowl.