snap cutter
I think your best best is to rent a rachet snap cutter for the cast, and cut in some tees.
One a cleanout tee, and one a 3x2 or 4x2 tee.
These can be assembled in the line using no-hub couplings. You normally leave about 1/4" gap so you can slide the tees in.
If you have cast, then I like getting cast tees, the sizing works better with existing cast.
Measure the outside diameter, old cast is 4-1/8" for a 4" line, new cast is 4-3/8" for a 4" line. With the smaller pipe size that is 4-1/8", you use a no-hub sized for copper pipe. If you cut in new fittings, that looks like a copper to cast size. The copper goes over the old cast, the cast size goes over the new fittings.
Put the AAV between the stack, and the p-trap.
Terry
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