Well, I have the slab poured and my 4" is sticking out the side of the footing and is connected to a kelly fitting. The stub end is a 4" pipe with a knock-out.
By the way all my connections held pressure.

About 5 feet away co-linear +/- is the 4 inch to the septic tank. It has a cap.

What is the best way to connect these stub ends?
How do you slip couplings in there with a pre-measured perfect length of 4" and then rotate it with primer and glue?

Thanks

I would use a 4" PVC coupling on the cleanout end and a shielded metal band,(see image) to join the other two. Good luck, Tom