Also known as the toilet float, it is as simple as it is effective, and has been a staple. 1 Change the Water Level in a Toilet Tank; 2 Adjust the Fill Valve of a Toilet .
The water level should be about a half inch below the top of the fill tube. To adjust the tank's water level, first adjust the fill valve. This is done by moving the float that's attached to the valve in the direction you want the water level to go, so raising it raises water levels and vice versa.