Just to add to what Terry said above about stacking the white rings/wafers and NOT to do it....
Looks like I found the source of occasional sewer smell in my basement bathroom (see pictures).
The EXISTING set-up is detailed below, but even with 3 extender rings, it still resulted in the toilet flange being approximately 1/4 - 3/8” BELOW the finished floor surface, instead of ~3/8” above it. Thus, a gap of ~up to 3/4” was left to be sealed with a single standard wax ring. You can see how well that worked out. Everything I know about this house tells me this has been going on for approximately 9 years.
I’m curious about the appearance of the failed wax ring...Looking at the rear portion of the ring (top section in photo), it seems to have been “eaten away” by the flushing water. Presumably making the already bad situation (3 stacked rings) even worse with each flush......? Or do you think the wax ring has always been concave in that area, as a single regular ring wasn't big enough to cover the gap, and not sealing right from the get-go? It does seem odd to me that it is the rear that looks like that, as the front would be subjected to more force by the water due to the orientation of the TOTO rough-in connector. But perhaps there was enough wax there to resist it and that isn't the case at the rear.
With everything stripped down to the slab I have a discrepancy of about 1 - 3/16” to deal with. That being the distance from the TOP of the existing ABS flange, resting on the concrete, to a new flange surface, resting on top of the replacement foam/subfloor/finished flooring build-up.
I will be reinstalling using a Sioux Chief Pushtite gasket flange, which has a clear smooth shaped opening, measuring 2 - 1/2" in diameter. Installing that on top of the new subfloor and vinyl, then using a single wax ring. Not easy to find in Toronto, Ontario, but I tracked one down, although I have quite a bit of work to do before I get to that point......*sigh*
DETAILS OF EXISTING SETUP for those interested:
Flooring:
3/16” Vinyl flooring
3/4” OSB Subfloor
1” rigid foam
Concrete slab
Plumbing:
ABS flange sits ONTOP the original concrete floor.
3x white spacer rings, stacked with no glue/gasket/silicone between them and not screwed down
Single “regular” thickness wax ring
TOTO rough-in connector (CST414)