Step 2 · Remove the Existing Drain Stopper
For the assumed push-and-pull stopper, ensure it is in the open ('up') position. Firmly grip the round knob on top of the stopper and rotate it counter-clockwise to unscrew it. If it's tight, you can wrap a rag around it and use pliers for a better grip. Once the knob is off, you will see a brass post with a slot in its center, which is threaded into the flange's crossbars. Use a large flathead screwdriver or the tips of your pliers to engage this slot and unscrew the post by turning it counter-clockwise until it's completely removed.