Hey all,

I am remodeling 1 full bathroom and setting up a tie-in for another future full bath. I removed most of the existing cast iron stack which was 3", and just as it enters the basement slab it transitions to 4". My plan was to reinstall the stack all as 4".

If you look at the attached photo, the 4" hub you see right at the floor level is the top of a 90deg. fitting. I was thinking I good cut off the hub and use a rubber coupling to tie into it, this would still require me to open up the slab. My questions are:
- do you see any issues with attaching a rubber coupling to the top of a cast iron 90deg sweep fitting (with the hub cut off)?
- would I better off removing a larger section of the slab and removing that 90deg fitting completely - then tying into a straight length of cast iron?
- am I making too much work for myself trying to upgrade the size of the waste line, and should just use 3" pipe and tie into what you see above the slab? (note I have already purchased all of the 4" pipe and fittings).
- note that the 2" galvanized line you see coming in services 2 sinks and potentially a future washer machine
- note the 90 fitting turns back into the house toward the direction the photo is taken from, so I don't have to be concerned with having to work in/underneath the foundation wall

Thanks in advance for any advice,
Sean

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