Drain Remaining Water and Block Drain

What happens here

Once the main water supply is off, turn the shower faucet handle to the 'on' position to drain any remaining water from the pipes. This relieves pressure and minimizes water spillage during cartridge removal. Then, place a rag or a drain stopper into the tub's drain. This simple precaution will prevent any small screws or parts from falling down the drain during the repair.

Goal: Prevent water mess and loss of small parts.