Drop-in Kitchen sinks are one of the most popular sink types. It is also often called a top-mount sink or a self-rimming sink. A drop-in sink is common in that you set it into the bathroom sink or the kitchen sink cutout in the countertop. Unlike an undermount sink option, which you install from underneath the countertop, the drop-in sink rests on the kitchen countertop after you lower it into the cutout.