Valves are available at most hardware stores. A leaking flush valve permits hidden internal toilet leakage. Dye testing procedure for internal toilet leakage. Place food coloring in toilet tank. Wait 15 minutes.
Color appearing in toilet trap signals a leak.
While you have the tank cover off, be sure to check the high water level. Tremendous quantities of water can be wasted if the water level reaches the top of the overflow tube. The fill level can be lowered by gently bending the float arm. The ballcock assembly occasionally becomes worn or fouled with scale, preventing shut-off of the water supply at the desired level. A few dollars invested in improved water efficiency can yield substantial annual savings.