The hardest part of installing a pop-up drain in an existing sink is maneuvering beneath the sink to do it.

Step 1: Remove the sink’s drain trap and old pop-up assembly. If necessary, hacksaw the old assembly apart slightly above its ball rod inlet.

Step 2: Use a damp cloth to clean the sink opening.

Step 3: Unscrew the top portion of the new drain and set the bottom portion aside.

Step 4: For porcelain sinks, roll a fair amount of plumber’s putty into a six-inch-long, half-inch-thick rope and press it onto the underside of the top portion’s flange. For fiberglass or stone sinks, place a thick bead of silicone caulk on the underside of the flange.

Step 5: Press the top portion of the drain into place, ignoring the putty that seeps out around it. If using silicone, wipe excess away immediately.

Step 6: Screw the lock nut, flat side up, onto the bottom portion of the drain assembly and slide the rubber washer onto the assembly. The domed side of the washer should be facing up.

Step 7: From beneath the sink, screw the bottom assembly up into the top portion of the drain.

Step 8: Once the two parts are tightly joined, turn the bottom portion of the assembly slightly so the ball joint inlet of the drain is pointing to the wall at the back of the sink.

Step 9: Press the rubber washer up to the base of the sink and tighten the lock nut into place, using a pipe wrench if necessary. The nut should be tight enough to seal the drain opening, but not tight enough to break the drain pipe.

Step 10: Wipe away the excess plumber’s putty or silicone from inside the sink.

Step 11: Drop the new drain stopper into the drain hole with the eye of its stem facing the wall at the back of the sink.

Step 12: Place the top portion of the pop-up rod into its hole on the faucet.

Step 13: Beneath the sink, insert the ball rod into the ball rod socket on the drain assembly and hand tighten the nut.

Step 14: Follow the drain assembly manufacturer’s instructions to attach the pop-up rod to the ball rod.

Step 15: Test the pop-up assembly and re-install the drain trap.

Step 16: Check for leaks and make any necessary adjustments.