Hi and thanks for reading.

Please bear with me as I explain the situation.

I have a 56 year old cape with a 4" cast iron stack down to the sewer line with, from the bottom-up starting at the foot of the slab:

1) A 3.5" cleanout

2) A tee-off for the sink/dishwasher drain, which loops back to the next element ... my guess would be 1.5 or 2".

3) double tee (same size as the drain in #2), one side is the vent for the sink dishwasher, the other side is the vent for the 2" washing-machine drain that connects below the cleanout via a u-trap buried underneath the slab.

Of course, somewhere under there is the ground-floor toilet connection, which is directly opposite the bottom clean-out.

I'm building a bathroom upstairs where there nary 'twas one before ...

Now of course, the right thing to do would be to have someone who knew what they were doing come in, dig up the slab and give me a new stack coming off at or below where the ground-floor toilet connects to the existing stack.

Not gonna' happen ... this place had a mold problem that set me back like 30% of my budget already. That was two years ago.

So the way I see it, I've got two options, neither of them good, but I'd like opinions as to which one would be less bad:

Option #1: hook into the clean-out at the bottom above the slab. I guess I'll need a 3.5"-3" bushing. Interesting side question: the cap is brass but the pipe is iron, **** things really rusty as it is ... should I use a brass or an iron bushing?

Option #2: tie-into the pipe from above (cut at a point between the floors, add a fernco). I thought about this and it would seem to me that if there's a toilet draining from above, that I'd have to cap the two 2" vents that I described, as since there's no water flowing through them, then this would create an unsanitary condition. I'm hoping that since there's water flow through the 2" connection below that for the kitchen sink and dishwasher that what I'm worried about for the vents wouldn't apply. I'd reconnect the vents of course, but above the upstairs drain tie-in.

Looking forward to any and all criticism. No feelings left here to hurt