I have a 4" cast iron waste stack that connects directly to the sewer line exiting the house. The stack consists of three separate sections all with a bald and bell ends. Each is leaded into the next. I would like to remove two of the three sections and connect PVC into the remaining section so I can run new plumbing. The section remaining would have the bell end exposed. Two questions: 1). How do I safely remove the two cast iron sections without damaging the third? 2). What fitting would I use to connect a 4" PCV bald end to a 4" cast iron bell end?

I would use a plum-quik rubber coupling. Id leave a few inches of cast iron on that "bell end" so that I have a regular end to fasten the rubber couping. I wouldn't remove the pipe out of the old cast iron bell housing, I would just cut it a few inches above it and connect that rubber fitting.

Bear in mind cast iron pipe is very heavy. No matter what method you use, make sure its supported so when you do remove your sections, it doest come crashing down ontop of you.

Its been said here that you can buy sawzall blades just for cutting cast iron, I haven't tried that, but it couldne be worse that what I did try. A cast iron sewer stack is my least desirable thing to cut into. Just wait until the sawzall blade starts spitting that raw sewage back in your face. (yuck)