Larry, Erik.

Please consider the porcelain insulators in your truck's engine.
Starting on a cold day, they are subjected to ~0 C to ~2000 C
once per revolution. They don't crack in normal use, yes?

The technique is to pour the ~100 C water down the center of
the bowl, raising the contents to ~50 C or so, lowering the
viscosity of the load. It might take 2 or 3 tries for the most
challenging ex-chimichanga but it always works, in my experience.

And it won't damage the plumbing.

--Winston

Spark plug insulators are for real porcelain, and designed for such
service. To this day I have difficulty 'wrapping my head' around the
conditions they normally operate. I agree, they are one of engineerings
great, unsung marvels.

I'm reasonably certain most, if not all toilets are in reality 'vitreous
china', and I'll bet money they aren't stress relieved in the mfg
process. Too expensive...

Check this:

http://en.wikipedia.org/wiki/Toilet

Look down near the bottom of the article under the heading 'How They Are
Made'

Erik