Remove Entire Old Drain Body

What happens here

Given the severe buildup, corrosion, and leaks in the existing drain system, the decision is made to replace the entire drain assembly. To do this, use a pair of adjustable pliers to unscrew the large retaining nut that holds the drain body to the sink from underneath. The presenter notes the pliers are like the "best adjustable job wrench ever," implying a high-quality tool. Once the nut is fully unscrewed, carefully pull the entire old drain body out from the top of the sink. This will likely reveal extensive grime, hair, and debris within the drain pipe. Thoroughly clean the sink's drain opening, removing all old plumber's putty or sealant residue, to prepare for the new drain.

Goal: Remove the entire old, corroded, and clogged drain body from the sink.