ballcock
/ˈbɔlˌkɑk/
noun
- A device in a toilet tank or other water tank that uses a floating ball to control the water level by opening or closing a valve.
- The plumber replaced the old ballcock to stop the toilet from running constantly.
- I learned how a ballcock works by watching the float rise and shut off the water.
- When the ballcock gets stuck, the water keeps flowing and can overflow the tank.