How to Plumb a Kitchen Sink with a Kitchen Sink Plumbing Diagram Unscrew and remove the metal drain flange from underneath the sink. You may have to use a pipe wrench or pliers to loosen it. If you see any water stains under the sink, soak them up with paper towels or a sponge. STEP 3 Remove any silicone caulk or putty from around the edge of the countertop opening with a putty knife.