Sometimes you need two wax rings, and that solves your problem.

This is the original floor.  There was a torn lead sleeve which I removed.  It was not there for the other toilet so I think it took the place of the plastic part of a wax seal.  In any case, I removed it.  I've tried the rubber donuts and they seem problematic to me.  But they did not leak and you could reposition the toilet.  It just never allowed the toilet to settle down solid on the tile floor. 

I used a similar one.  The problem was that the toilet rested on the resilient rubber and never wanted to settle down on the solid floor.  I was afraid to tighten the bolts enough to do so.  I worried that the porcelain would fracture.  I ended up putting spacers under the toilet to get it on solid ground.  But it did not leak.  I tried a similar one before the wax ring and that leaked too.  So I am waiting for the plumber.  I'm done lifting 80 pound toilets in and out of a tiny bathroom.

Why give up, just go buy another thick wax seal and try again. Some folks double the wax rings. Also make sure it is the right direction, unlike how the photo above shows it with the plastic part facing up.

The last time I changed a wax ring was probably 10 years ago, when I was 63.  My back did not complain at that time.   

This time my back did complain.  I have more money than backs, so I will await the arrival of the plumber. 

I deliberately chose the image with the wax ring upside down to illustrate the plastic insert that I was referencing in the post.  I did install it facing the correct direction. 

It is likely that I needed two wax rings.  It settled down a bit too easily and quickly.  I expected to have to push it down into place.  Instead, gravity was all that was required.

         ^ Almost a certainty.  ^

When I replaced mine I ended up going with one of the non-wax manufactured ones. I don't remember which one I used but I do remember that they are not all created equal. After some research I chose the one that I thought would work best. It has been about seven years ............... so far no problems. Advantages are ...........  variable thicknesses, more adjustable, if you don't get the position it quite right ( bolts lined up, etc)  you can try again or wiggle it into place more easily, take it off and change the thickness.  With the wax it is pretty much a one shot deal. I tried a wax ring first and had nothing but trouble getting it pushed down and aligned correctly.

Seth

I constantly have leaks in our subfloor mounted toilet. I have even double sealed it. I'm pretty sure the floor & or the toilet is not flat. I have to use the shims shown above. I use double wax seal and also remember to warm them up a bit as instructed. Since this location is on a cement slab I'm actually considering just caulking if it leaks again. Other two toilets in the house are no problem at all.

The last time I changed a wax ring was probably 10 years ago, when I was 63.  My back did not complain at that time.   

This time my back did complain.  I have more money than backs, so I will await the arrival of the plumber. 

Now that's funny...and I can relate to the age/back thing also.

I constantly have leaks in our subfloor mounted toilet. I have even double sealed it. I'm pretty sure the floor & or the toilet is not flat. I have to use the shims shown above. I use double wax seal and also remember to warm them up a bit as instructed. Since this location is on a cement slab I'm actually considering just caulking if it leaks again. Other two toilets in the house are no problem at all.

Not an expert but I think I’ve read that you should bed the toilet in a ring of plaster when the floor is not flat. Tighten the bolts after the plaster sets. I guess you could butter the porcelain base with Vaseline if you’re worried about plaster sticking to it forever

I’ve gotten into the habit of always using a JUMBO wax seal. The plumber I apprenticed for said to always use the thicker one. You can get them without the horn, (the plastic funnel piece), but we always used the ones with.

Don’t remember ever having one leak, but mostly did new installations so our stuff was setup for success from the getgo.

So the toilet is installed for a month now and it has proven capable and reliable. 

I was very limited as to which toilet I could get on short notice because it backs up against a baseboard hot water heater, and I needed the clearance.  Most of the toilets have a flat flange that goes all the way back and would have interfered with the baseboard heater.

I ended up with Lowe's own brand (Project Source) toilet.  I was a bit leary as it was very cheap (about half the price of the Kohler unit I installed last year) at $99.00 + tax. 

It uses Fluidmaster components, so at least replacements will be easy to find.

By all appearances (except the quality of the plastic seat) this is the equal of the Kohler unit.

When I opened the box the hinge on the toilet seat was broken.  Lowes replaced the seat with one stolen from another in stock toilet.  It is flimsy and moves side to side and does not feel stable.  I got a Kohler soft close seat with the capability to be instantly removed if cleaning is required (put the toilet seat in the dishwasher? ).  In any case I had the same type of seat on my old toilet and it was very good.  I will install it this weekend.

So this becomes "recommended".  It works well, and I was two-bolts-not-tightened-enough away from a successful install.  And it is a really excellent value at $99.00.

https://www.lowes.com/pd/Project-Source-Project-Source-Pro-Flush-2-Piece-Single-Flush-Elongated-Chair-Height-White-1-28-GPF/1003066162

The old toilet used far more water and took far longer to refill.  The flappers required were hard to find and would intermittently stop sealing closed, and would run water all night if I did not use it.  And apparently the previous owner broke the tank lid and bought a replacement which did not quite fit. 

So, all in all, I was happy when the thing finally needed to be replaced.  I was not happy with the process however.