Drop the pop-up stopper into the sink's drain opening, allowing the stopper to sit in the closed position. Insert the narrow end of the lift rod into the hole in the top of the sink's faucet.
Allow the sink's lift rod to drop until the handle on the top rests on the top of the faucet. Slide the U-shaped end of the clevis over the narrow end of the rod.
Twist the retaining nut on the clevis clockwise to securely attach it to the lift rod. Slide the circular retaining nut over the long, narrow end of the pivot rod, making sure the threads on the nut point toward the end of the pivot rod that is shorter and has a ball.
Insert the long, narrow end of the pivot rod through one of the holes in the clevis. Insert the narrow end of the pivot rod into the opening in the sink's drain pipe, stopping once the large ball on the pivot rod sits inside the pipe.
Slide the retaining nut on the pivot rod into the opening in the sink's drainpipe. Thread the retaining nut on the pipe's opening by twisting the nut clockwise. Fill the sink with at least an inch of water to make sure the stopper seals correctly. Adjust the stopper by threading the end of the pivot rod through another hole in the clevis.