Bath Remodel Adding Shower and WC

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SLOJim

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Feb 6, 2025
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San Luis Obispo, CA
My wife and I have been remodeling our 1963 house for the last 25 years and we have finally gotten around to our bathroom. Yeah, we are a little slow. It's single level with cast iron horizontal line under a far too thin concrete slab that then transitions to a clay pipe lateral once it clears the slab. Over the years the original shower pan failed and was replaced with a tub at the expense of the toilet. Our plan calls for cutting into the 3" cast iron and adding a toilet and shower. I am both totally new at DWV design as well as forum usage so I apologize ahead of time for the many mistakes I am about to make.

The cast Iron horizontal run has been scoped out and looks solid and clear and should be 24 inches below the slab. My goals are, in order of priority:
1) Obtain the best draining and venting using a single 2" vent.
2) Provide a full size cleanout hidden in cabinet for new 3" section.
3) Minimize slab destruction/reconstruction.
4) Be code compliant with CA 2021 pluming code which is based on UPC 2021

Below you can see the original layout and what I hope to finish with. In the original, the (red) shower was removed. The underslab connections to the 3" are assumed with help from video scope.
1739129525751.png
In the future layout below red toilet shower combination is what I plan on adding.
1739129578364.png
My instinct to keep it simple keeps coming back to the layout below where both the shower and the WC drop into the same vertical which is also the the same pipe that has the cleanout and the vent stack headed for the roof. It is so simple and obvious that it can't possibly work. But here it is anyway as option 1:
1739129837875.png
1739129891555.png
The next option in my mind (Option 2 ) moves the WC connection from the Vertical pipe to the horizontal while still keeping the shower feeding into the vertical pipe.
1739130053922.png

1739130159881.png

I apologize again for the giant data dump. How close am I? If either of these are close my next step would be an exploratory hole to verify the 3" cast iron pipe location, conditions and depths are accurate. Then it's commitment time. I am trying to make sure I am using the correct fittings and taking the correct path before tearing into the slab.

Thanks in advance

JIm
 

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