Step 6 · Tighten Compression Nut
With the new valve hand-tightened, it's time to create the permanent, watertight seal. As before, you will use two wrenches. Use one wrench (channel-locks or adjustable) to hold the new valve body steady, ensuring its outlet is pointing in the correct direction (usually straight up towards the faucet connection). Use your second wrench to tighten the compression nut. Follow the manufacturer's instructions, but a general rule is to tighten the nut one-half to one full turn past the point where it was hand-tight. You will feel the ferrule compress and bite into the copper. The goal is to be tight enough to seal, but not so tight that you damage the pipe or valve. Do not over-tighten.