Step 4 · Remove Sink Flange and Mounting Hardware
From underneath the sink, locate the three screws on the remaining mounting assembly. Loosen these screws until the lower part of the mount (the backup flange) can be removed. Next, you will see a thin, springy metal snap ring holding the rest of the assembly in place. Carefully pry one end of this snap ring out of its groove using a flathead screwdriver. Be cautious as it can spring off unexpectedly. Once the snap ring is off, the rest of the mounting hardware will come free. Move to the top of the sink. Use a putty knife to gently pry up and remove the old sink flange (the metal drain piece). Scrape away all the old, hardened plumber's putty from the sink's surface. For a perfectly clean surface, wipe the area around the drain hole with a cloth and a small amount of rubbing alcohol.