If you are not getting a full flush or the water is continually running in your toilet, it might be time to adjust the water level. Adjusting the toilet tank water level with a Fluidmaster Model 400 fill valve does not require turning off the water to the tank. The fill valve uses a float that moves up and down the valve rather than a float ball. Adjusting the valve adjusts the amount of water that comes into the tank after flushing.
Take the lid off the toilet tank and set it aside on a flat surface. Look for the waterline mark on the inside rear of the toilet tank. The line is either a short blue line or a short engraved line in the tank. This is where the water level should be when the Fluidmaster Model 400 stops filling the tank with water.
Find the thin steel rod along the side of the fill valve. The rod attaches to a lever on the top of the fill valve and inserts through a spring clip attaching to the side of the fill valve float.
Grasp the spring clip between your thumb and forefinger. Squeeze the clip together to move the float up or down the steel rod as necessary. Move the float up to increase the fill water or down to decrease the water level.
Flush the toilet and check the water level when the fill valve stops filling the tank. Adjust as necessary. Put the toilet tank lid back onto the tank.
Move the float in small increments when making adjustments.