Clean or Resurface Valve Seat

If replacing the washer doesn't stop the drip (especially in older compression faucets), the valve seat (where the washer seals) might be corroded or damaged. After disassembling the faucet stem, inspect the valve seat inside the faucet body. Use a cloth to clean away mineral buildup. If it's pitted, use a valve seat dresser tool to grind it smooth. Reassemble with the new washer.