On Tuesday, April 2, 2013 1:32:36 AM UTC-4, Danny D. wrote:
So, I have the $75 internal pipe wrench on order.

That is a colossal waste of a perfectly good $75 for a perfectly useless tool in this case.

You do NOT want to try extracting that nipple with an internal pipe wrench. You are only setting yourself up for an even bigger job as you chase broken drain pipes up and down the wall cavity until you finally give up and call a plumber, which you should've done in the first place.

The nipple is corroded and will crush easily with some big pliers. Once you collapse it it will peel right out leave you a nice undamaged thread for the new nipple.