https://www.askmehelpdesk.com/plumbing/cutting-cast-iron-drain-pipe-257290.html
Hi there,
I'm a first time user and have just been reading through a lot of posts and being amazed at how much info is here and what great and thorough answers! I am remodeling a 1 story home in Tennessee and have it torn down to the studs at the moment. Its about 70 years old. I have a main drain line(horizontal) that comes in from the street underground and then emerges under the bathroom where it connects to the main vent stack and drains from the toilet, shower and bathroom sink.(all cast iron) Most of the connections on the main stack are old and some have come apart. I would like to cut out the cast iron from the main pipe as far as I can and redo all with PVC.
I came across what seem like instructions for doing this at the post below:

https://www.askmehelpdesk.com/plumbing/cutting-cast-iron-drain-pipe-257290.html

My question is is this really all I have to do? Just cut the cast iron and use the couplings and bushing mentioned, and then just replace what the existing drain lines that I see with PVC in the same configuration that I currently see the cast iron in?(new fixtures will go in same place as old fixtures. ) I'm sure you might need more info to answer question, but I'm not sure what. Just let me know what else you need to know and I can get the info and pics if that would help.

Thanks so much!

Jeff, you said it: Cut old CI pipe and copy it with new PVC pipe and fittings. Just be careful so the upper portion of stack will not fall on your head. Support it with 2x4 frame before you cut.