With a few tips and some good advice, for which I am thankful, I am ready for step three of a drain replacement. The old (68 years old) 1.5 inch steel line is suffering from wall build up. I have changed the bathtub drain and vented the bath P trap, changed the bathroom sink and all the drain line up to the last 3 feet. Which has moved the bottle neck to the last leg of the pipe. New ABS is attached to the old steel with a shielded clamp for now. I am a little worried about damaging the old stack while pulling the last leg of the galvanized pipe. Any suggestions or warnings before I attack this? Am I best off to start with a pipe wrench or go straight to a nipple remover or internal wrench? I assume there is a pretty big risk the nipple is rotted inside and needs to be cut out. Any advice is greatly appreciated.