Step 7 · Final Tightening and Leak Test

This is the step people usually slow down on. Go finger-tight first, then a quarter turn. No rush — replay the clip whenever it helps.

Go back and check all the connections you made: the mounting nut under the sink and all the slip nuts on the P-trap and tailpiece. Hand-tighten them as much as you can, then use channel-lock pliers to give each nut a final quarter to half-turn. Be careful not to overtighten. Now, it's time to test for leaks. Close the sink stopper and fill the basin with a few inches of water. Let it sit for a minute to test the flange seal. Then, open the stopper and let all the water rush through the drain. As the water flows, carefully inspect every joint and connection with your hand and a flashlight for any drips. Check the P-trap nuts, the tailpiece connection, and where the trap arm enters the wall. If you find a leak, tighten the corresponding nut slightly. If it persists, you may need to disassemble the leaking joint and check that the washer is seated correctly.