To replace a toilet water supply line, follow these steps:
Shut off the water supply: Locate the shut-off valve behind the toilet and turn it clockwise to stop the water flow.
Empty the tank: Flush the toilet to drain the water from the tank and use a sponge or towel to soak up any remaining water.
Disconnect the old supply line: Use an adjustable wrench to loosen the nuts connecting the supply line to the shut-off valve and the fill valve on the bottom of the tank. Remove the old supply line.
Install the new supply line: Apply plumber's tape to the threaded ends of the new supply line. Connect one end to the shut-off valve and the other end to the fill valve. Hand-tighten the nuts, then use the wrench to give them a quarter-turn to ensure a secure connection.
Turn on the water supply: Slowly turn the shut-off valve counterclockwise to allow water to flow into the tank. Check for any leaks at the connections and tighten if necessary.
Remember to check for leaks after turning on the water supply and to verify that the toilet is filling properly. If you encounter any difficulties or are unsure about the process, it's recommended to consult a professional plumber for assistance.