Our house was originally constructed in 1957 with a mix of galvanized and cast iron for drain pipes. In 1970 the previous owner did some remodeling and used copper drain pipes. Now it's our turn to remodel...

The photo below shows the drain pipes from our bathrooms and laundry room. We believe the drain pipe under the slab is cast iron, with a cast iron hub at the floor slab. There's a copper drain pipe tying into that CI hub - you can see the corrosion where the metals meet.

Our replacement drain pipes will be PVC.

Can we cut the copper below the T, leaving a 2-inch stub of copper, and tie our PVC drain into the copper with a Fernco fitting? Or do we need to bust out part of the concrete slab and tie the PVC into the CI below the slab (so as to remove that corroded hub?)

Thanks for any advice or ideas you can provide.

Drain assembly, looking east

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Close-up of corrosion, looking east

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Close-up of corrosion, looking west

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