For some reason, the builder put in the toilet flanges in my 5 bathrooms so
that the top of the flange sticks up 3/4" above the tile floor. The toilets
he put in apparently had a deeper inset and did not rock. As I am replacing
the toilets, I find that new toilets have only a 1/2" recess around the
outlet. This makes the new toilet sit 1/4" above the tile floor. (3/4"
protruding height less 1/2 " recess). A also need about 1/4' for the
compressed wax ring, leaving me 1/2 " from proper seating of the toilet.

The sewer outlet pipe is 4" ABS, coming up through the concrete slab. The
ABS flange is glued to the *outside* of this pipe. The flange is not screwed
down, just sitting there.

I propose to cut off the flange/pipe level with the tile floor, using an
angle-grinder. I will then glue an *inside* flange into the 4" pipe. The new
ABS flange is 3/8" thick and will sit directly on the tile floor. I should
gain 3/8" using this approach, which should be enough to seat the toilet
properly.

Does this make sense?

Walter
www.rationality.net