Measure the length of the old faucet from the connection point to the exterior flange. If upgrading to a frost-proof model, measure the thickness of your wall from the interior pipe fitting to the exterior wall surface. Purchase a new frost-proof sillcock of the correct length (e.g., 8-inch, 10-inch, 12-inch). The new faucet must be long enough to extend through the wall and connect to the pipe. Clean the threads on the interior pipe fitting using a wire brush to remove old pipe dope, tape, and any corrosion. Ensure the opening through the wall is clear of debris.