I put some of Graybeard's chili in my pot, sloshed it around for a few seconds (any longer and the pot will disappear) and then poured it out. Cleaner than a whistle!
Seriously, I avoid the use of Marvelux flux, despite claims that it works so well. It leaves a hard, gray deposit in my pots that's the Devil to get out. Also, I don't see that it works any better than traditional fluxes.
I still use a bit of bullet lubricant, beeswax or lard to flux my lead.
When deposits build up, I empty my pot. Then, I set it at its lowest setting and leave it there for about 5 minutes. This seems to loosen the scale somewhat.
Then I turn off the heat (don't want to burn out your thermostat) and scape down the sides with an old, heavy spoon.
Cheyenne Ranger mentioned the use of a putty knife and that seems like a good idea. I'll have to try that. I think a narrow one would be especially useful.
I haven't tried the boiling water method. That sounds intriguing.
A very good post with interesting answers. Thanks for bringing up a good question.