Currently I have cast iron drain system. All plumbed fixtures are on the 1st floor of the house. I want to add a basement bathroom which will require jack-hammering up the slab and tying into the waste line. Can I leave the old cast iron stack for the rest of the plumbed items or will I need to replace it with ABS? I'm worried about the weight of the stack if I break up the slab and disturb the soil in which the stack is currently sitting. There are some old pipe straps on the stack but they look more for balance that weight support. Also, all my clean-outs have sealed solid shut over time. Do I tear out the stack and redo everything or leave the stack and just tie into it underground for the basement bathroom?