Moving toilet location in basement slab.
I have removed all the concrete and am ready to move the waste pipe for my toilet. I currently have a Sioux Chief TKO toilet flange (model 883-AT) installed and I will be replacing with the same. www.siouxchief.com/PDF/TKO-Brochure-4- 05.pdf
This flange can go inside 4" pipe or over 3" pipe. Hopefully I can explain this properly. Currently, the set-up is the flange is installed inside a 90 degree elbow with 4" opening that reduces to 3" that connects to the waste line. The problem is that I cannot find this 4" to 3" reducing elbow at Home Depot or Lowes. Is it OK to simply put the flange over 3" pipe or is there a reason it is set-up this way in the basement slab? The set-up on the other bathrooms I have is the same flange goes over a 3" 90 street elbow connecting to the waste line. The basement slab install is the only one that connects into this 4" to 3" reducing 90 elbow.
Thanks for any assistance you can offer.