The drain plug, or stopper, in the bottom of your sink allows you to contain water in the basin for washing or other purposes. These plugs are controlled by a series of levers that raise and lower the plug in the sink. Removing the drain plug from a sink is necessary if you need to unclog the drain. Because the drain plugs are attached to the lift lever, it's necessary to unhook the lift lever first if you want to remove the drain plug from the sink.
Press the pop-up lever down so that the plug pops up in the sink. Wedge a small piece of plastic or wood between the bottom of the stopper and the drain. This will help keep the drain open while you work.
Disconnect the push lever from the lift bar. Position yourself under the sink. Follow the vertical push lever from where it leaves the bottom of the faucet to where it meets the horizontal lift lever. Where the two meet, you should see a small spring clip. Squeeze the sides of the spring clip together to pull it off the lift lever.
Follow the horizontal lift lever forward to where it meets the straight piece of pipe coming from the drain above. Where the two meet, you will see a coupling holding a ball valve in place. Unscrew the coupling, using the pliers if necessary. Pull the lift lever out of the tail piece.
Grab the small piece of plastic or wood with your fingers with one hand. With the other hand, remove the drain plug from the sink.