Sink drain stoppers trap water in the bathroom sink so that you can use it for washing or any other needs. The stopper is connected to a lift lever beneath the sink, which connects at the straight piece of plumbing located just beneath the drain. A push lever located on the faucet moves the lift arm up and down, which opens and closes the stopper. Replacing a bathroom sink drain stopper isn't difficult, but it is a little tricky getting the sink stopper reattached to the lift lever.
Lift up on the pop up lever so the pop up stopper opens up in the sink.
Position yourself beneath the sink. Locate the pop up lever, which is the horizontal metal bar leading into the sink plumbing. Follow this to where it meets the drain and you will see a coupling. Loosen this coupling.
Grip the pop up drain with one hand and the horizontal pop up lever with the other. If this is a large sink, have an assistant grab the drain.
Pull the horizontal lever out of the plumbing pipe. This will release the pop up stopper, which can now be lifted up out of the drain.
Insert a new sink drain stopper into the drain. Now comes the tricky part: reinsert the horizontal lift lever into the sink drain pipe so that the end goes through the opening at the end of the pop up stopper. You may have to make more than one attempt at this.
Secure the coupling in place once the pop up stopper is secure at the end of the lever.
Use a pair of pliers to help you loosen the coupling in Step 2, if needed.