Step 1 · Turn Off the Water Supply and Drain the Lines

Before you begin, safety first! Turn off the water supply valves under the sink. These are usually separate valves for hot and cold water. Then, turn on the bathtub faucet to release any remaining water pressure in the lines. This prevents a mess later. Depending on your setup, you may need to access the water supply lines from behind the wall; have towels handy and consider enlisting help.