We (my son & I) are remodeling a 50s bathroom, and creating a new half bath in a newer (90s) master bedroom. The old toilet needs to move, about 6 feet from its current location. The new one will be about 12 feet further from the original drain. The existing setup is all 4" cast iron, down into a 'T' connected to the vent right beneath the flange. The huge 4" T goes from the bottom of the 2x6 joists to the ground surface, there attached to the presumably cast iron sewage drain (actually, a septic system.)

Can the cast iron be removed, and replaced with sch 40? Uh, how? Should we dig down a bit to expose the drain pipe, then cut it off? If so - What is the tool to use for cuttting? Given sufficient drop, can 2 toilets use the 1 drain? And 1 vent?
(Rotten subfloor has been removed, we have plenty of elbow room.)

We are fairly capable with normal DIY plumbing chores & fitting sch 40 runs and repairs, but this is our first 'rough-in' or major plumbing change. (We did the major remodel of everything except the bath in '90s, including kitchen sink, new toilet, etc.) Is this a task strictly for a pro, or is it feasible we handymen can handle it? Thanks.

If this were my job I would rent a set of cast iron ratchet cutters and cut the cast iron stack off a foot or so above the basement floor and convert to PVC using a No-Hub Band,(see image). I would then replace everything with PVC.
Yuu ask about vents, I assume the 1/2 bath will include a lavatory. This fixture will have to be vented and that vent will service the new toilet. You may use the 4" stack to pick up both bathroom gtoups. More questions? I'm as close as a click. Tom

Thanks! Today was more stump pulling outside (I'm also the backhoe driver.) Tomorrow we search for rental cutters...