i used to see a dump truck, that would be in my neighborhood, stop at the various meat stores, picking up the animal fats. i asked the driver once, if it was going to the dump, he said, no, they make soap out if it..
i was very young back then, so i thought it was gross.
we have a soap factory up here, http://www.bradfordsoap.com/
and again, a long time ago, another dump truck was dropping off the animal fats. For a while Bradford made, "Oil of Olay" don;t know if they still do, and they also made that fancy soaps you'd keep in a jar, to make the bathroom look pretty.