hi everyone, needing advise from someone who is knowledgeable about Chicagos strict plumbing code. All others need not reply. I'm replacing what a previous home owner did under ground in Chicago basement. They replaced 10' of 6" clay with 4" pvc and tapped into it for a bath. The hole is already dug up so I want to rip all the pvc out and replace with 6" clay as original. Can I do clay all the way up with a 90 and just stay below the concrete line and then lead in a 4" cast iron on top of the clay pipe? Or do I need to install cast iron directly at the 6" clay city line? full plan is to add the 6" x 4" clay wye, then add another 4" clay wye so I can stub up two clay 4" 90's. From there I'm going to lead in two cast iron stub ups and continue on with pvc. One of the stub ups will be for 1st floor bath and the 2nd stub up will be for other basement fixtures I.e new bath, laundry room, kitchen. Let me know if I can do the majority with clay. Thanks everyone.