At wits end with toilet.

Hi all:
Brand new Kohler Wellworth toilet. Moderately rusty 4" cast iron drain line and flange in a 3rd story condo.
Several installation attempts with new toilet resulted in leaking in the back of the base; definetly not sweating or tank seal leak.
Went out and bought a Ferno Wax Free Seal....cleaned horn and everything.
a) the !#*!)(#! seal wont stick to the bottom of the toilet. Clean, dry, etc...push it in...falls off in a few seconds....doesn't matter what I do...absolutely will not hold on its side or when I upright toilet to put it in.
b) for the heck of it, tried to put the seal in the drainline first....it doesn't fit....its like the drain line or the flange is really out 3 7/8" wide or 15/16". Absolutely cannot shove it in there.

At wits end with what should be an easy part of my bathroom project. All advice welcome.

I hope you are NOT trying to shove the wax seal INTO the drain line the way you indicate in your story. Either you are the worst "plumber" in existence, or you may have a defective toilet bowl.

No no I know what to do with the wax seal I just figured I'd try the the No-Wax Fernco Seal approach and see if I got better results, better seal, less mess, etc.
The no-wax fernco thing (like the fluidmaster one except my TrueValue stocks the fernco version) is what doesn't fit into the pipe, (not the regular wax ring)...Im not a master plumber by any stretch but I'm not *that* bad....

IT would NOT fit into a "moderatly rusty" cast iron riser, and even if it did it would NOT seal.

Wax is easier to work with.
If the flange is higher then the floor, you can use one wax ring.
If the flange is lower then the floor, you will want to stack two wax rings on the flange, and then set the bowl down on it.

Thanks Terry: Flange is slightly higher than the floor as it was just on top of old tile which has been ripped out, so its definetly a one-ring situation if using wax. In re-doing it with new wax rings a few times over the last several days, pretty much the same result every time. Leaks from the back.

I figured somehow I was just consistently not seating it well so the no-wax approach was worth a try....of course that doesn't even seem to be something I can try since the stupid thing won't adhere or fit right!

The toilet could be defective...wouldn't be the first time.

For whatever its worth, the American Standard it replaced (was old, not water efficient and prone to TANK leaks) never had this problem, and I did reseat THAT one myself with wax rings a few times without this happening. Since the part that changed was toilet (not me, the flange or the wax rings), I'd like to believe that's the toilet is the source of the trouble. Of course I wanted to get the wisdom of the experts here before coming to that conclusion and trying to exchage/return.

It could be the bowl.

If you try two different toilets and have the same problem it is the installer. If you install that bowl several times, and different ways, and still have the problem it is more likely to be the bowl.

BTW it apparently was the toilet. Replacement bowl and everything works hummingly with minimal fuss.