Step 4 · Apply Silicone Sealant
Lower the sink slightly by loosening the clamps. Using a caulking gun, apply a continuous, even bead of 100% silicone sealant to the top flange of the sink. The bead should be about 3/8-inch thick and unbroken all the way around the perimeter. This bead of silicone will create the primary waterproof seal between the sink and the countertop.