Mounting a Vessel Sink 1. Before you begin, make sure you have the correct vessel sink drain. If 2. 3. 4. the sink you bought has an overflow, then you will need to make sure you get a vessel sink drain with an overflow (PU11PC). A sink without an overflow will require a vessel sink drain without an overflow (PU22PC). Position the sink. Mount the vessel directly onto the countertop. Align it with the drain opening on the countertop.