Step 4 · Remove Old Mounting Assembly
From underneath the sink, use a screwdriver to loosen the three screws on the mounting assembly. Once loose, use a flathead screwdriver to pry off the metal snap ring that holds the assembly together. Be careful as the ring can be under tension. With the snap ring removed, all parts of the mounting assembly (mounting ring, backup flange) will come off. From inside the sink bowl, push the old sink flange up and out from underneath. Use a putty knife to scrape away all the old, hardened plumber's putty from the sink's drain opening. Clean the area thoroughly with a rag and cleaner to ensure a good seal for the new drain.