I need to tap into a vertical cast iron sewer to run a new wash machine drain. The old one is super slow and just won't clean out. I would rather not cut into the concrete basement
Floor.

I need to tap into a vertical cast iron sewer
Not something you want to do if you can avoid it.


The old one is super slow

Have you run a snake through it?
Does present washer stand pipe tie into stack above or below the floor?

It's MUCH simpler to unclog your drain than tap into it. What have you tried so far? How far did you snake? Where is your cleanout? Any other slow drains?

I agree with advices above. Avoid cutting Cast Iron.

But, with some effort, proper tools, skill and knowledge - it can be done. Assess your situation carefully. If you cannot clean your drain and / or it continues backing up even after cleaning - come back and we will guide you through cutting 4" Cast Iron stock and installing washing machine inlet.

Milo