• If you hear a sustained hissing sound coming from your toilet, it's probably a result of water trickling into the tank via the supply line. In this case the parts to check are the float, the refill tube and the ballcock or inlet-valve assembly.

    The hissing sound is typically caused by water coming through the inlet valve. First check to see whether the float is sticking or needs adjusting.

    Next, check to make sure the refill tube isn't inserted too far into the overflow tube. (It should extend only about 1/4" below the rim of the overflow tube.) If neither of these adjustments solves the problem, you'll probably need to replace the ballcock assembly.