These are pictures of my sink drain (chrome-plated brass) going into the wall. It attaches to cast iron pipe there. I need to remove the wall bend where it goes into the wall. Is that a slip nut at the wall (like the other two slip nuts in the picture), and is that all that attaches the wall bend to the cast iron? If so, I assume I can just unscrew that nut counterclockwise and pull out the brass pipe. Should I use some penetrating oil to loosen it up, or apply some heat, to help ensure that I don't twist the cast iron pipe? The yellow stuff is just insulating foam. Thanks.