On Mon, 01 Apr 2013 00:18:46 -0500 Vic Smith wrote:

Or pull the cabinet so you can get at it with a regular pipe wrench.

The cabinet is tiled in, so, that would be a ton of work!
(I'd rather remove the entire back by cutting it out!

sounds like you have a coupling on that nipple, since it's
female threads showing.

I must have explained badly as the PLASTIC horizontal tube after the P
trap is what has female threads.

The 1.5" diameter rusted nipple has MALE threads (not many, but my
fingernail can barely feel them on the 1/4" that is sticking horizontally
out of the back of the built-in sink cabinet).

You might look into using a Fernco connector on the stub showing, and
not have the work of removing/replacing it..

Googling for Fernco came up with PERFECT options for a clamped on fitting!
It's like a rubber car radiator hose! I like it. It probably needs more
bite than the 1/4" of rusted male nipple threads sticking out, but if I
cut a bigger hole around the pipe in the cabinet backing, I might gain an
inch of pipe to fit the Fernco on.

Thanks for that advice. Tomorrow, I'll head off to Home Depot to pick up
a Fernco and I'll look to see if they have the internal pipe wrenches!

I'll snap pictures for you to see the results.