The $5 Part Causing Your $200 Water Bill: How to Fix a Running Toilet Fast
Before replacing any toilet tank internal parts, address the two adjustments that require no tools at all. First, inspect the chain connecting the flush handle arm to the flapper. If the chain is too taut, it prevents the flapper from settling flat against the bottom rim, letting water bleed through continuously. If the chain has excessive slack, it can drop underneath the descending flapper during a flush, breaking the hydraulic seal. Unhook the clip from the trip arm, adjust the links until the chain has approximately one-half inch of slack, and reconnect it.
Second, inspect the fill valve adjustment screw or clip. If the water level reaches the very top rim of the overflow tube, water will siphon into the bowl indefinitely. Locate the plastic threaded rod attached to the float cup. Rotating this adjustment screw clockwise or counter-clockwise lowers the float cup height. Lower the float until the standing water line stabilizes precisely one inch below the rim of the hollow overflow tube. Flush the toilet once and observe the refill cycle. If the valve shuts off cleanly at the new marker, the problem is solved.
