Home-improvement pro Brad Staggs describes the best way to remove an old drop-in sink from an existing countertop.
When sinks like these are set place, they're generally glued down with some type of adhesive such as caulk. To separate the sink from the countertop surface, start by trying to cut through the edges of the adhesive using a utility knife.
If the blade of the utility knife won't cut all the way through the adhesive, try using a longer blade. Handles are available that hold a hacksaw blade as if it were a knife blade. Use the thin, flexible blade and fine teeth of the hacksaw blade to slowly cut through the seal all the way around the sink.
Once you've freed the sink and lifted it out, clean the remaining caulk from the countertop surface using a razor blade and some lacquer thinner.