Step 2 · Check and Adjust Tank Water Level

With the tank lid off, identify the water level. Most toilets have a line marked on the inside of the tank wall or on the overflow tube indicating the proper water level. If no line is visible, a good rule of thumb is for the water to be about 1/2 to 1 inch below the top of the overflow tube. A low water level means there isn't enough water volume for a powerful flush. Adjust the float mechanism to raise the water level. For older ball-style floats, you may need to gently bend the brass arm upwards. For modern cup-style floats, you'll typically find an adjustment screw or clip on the side of the fill valve that you can turn or slide to raise the float.