If you're planning on knocking out the main stack.... (first of all, be careful, know what you're doing, yadda yadda yadda...)
... you'll need to rent a pipe breaker - it's a tool that clamps around the pipe and cracks it evenly. A sawsall will not cut through a stack pipe (or it may take a few days to get through it.).....
Then, the rubber fittings and all still apply.
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