How to insert a WYE under slab???

I am adding a toilet and sink in my basement. I have a permit and have cut up the slab and have located the 3 inch ABS drain pipe. I know how the pipes will flow and I have a vent pipe located. Everything is ready but....
I am not sure how to insert the 3 inch Wye into the existing 3inch ABS drain pipe under the slab.
I know about a fernco fitting and bought one at Home Depot. It is a 3 inch plastic to plastic one that is all rubber with a clamp on each end. I think I read here those could not be used underground. Is that true?
My plan was to cut a section of the current 3 inch ABS out and leave room to attach a small stub pipe to one end of the WYE. Then slide the Fernco fitting over the other end of the existing pipe, insert in the WYE with the stub piece so there is about a 1/4 gap between the stub piece and the existing pipe and then slide the fernco over this 1/4 inch gap and tighten the clamps after I glue the WYE to the other existing piece.
Can this fernco fitting be used underground? Or do I need one of these with a metal sleeve? I keep seeing a picture od a PROFLEX fitting but can find none online.
Also, can someone tell me is a SLIP fitting would be better? It sounds better but seems like once I apply the glue you have to move really quickly to make it work.
Any help would be so appreciated.
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You are on the right track. You can use either Ferncos or no-hub band clamps. You will need 2 of them, one at each end. I doubt that you will be able to make up the connection on one end only. The glue hubs are larger than the pipe. You will either need ferncos with different ends or you will need to flue in short nipples of pipe. Slide the adapters onto the pipe after you cut out the appropriate section, install new piping, slide adapters and tighten.
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