Dr. Bill sent me a link to Take Our Word For It, and though I couldn't find what I was looking for, I did find:
What is the origin of hogwash? We are trying to settle a dispute among co-workers.

Ah, here we are again, mediators in workplace disputes. We should start a human resources business! As for hogwash, it is simply wash for the pigs. Wash in this sense is "swill", or "liquid or partly liquid food refuse from the kitchen". It's basically a bucketful of kitchen scraps and leftovers, and when given to the pigs that many country families raised once upon a time, it came to be known as hogwash. Eventually, hogwash came to apply to anything that was worthless, then worthless or bad writings, and now it seems to have taken on the meaning of "untruths". The word is first recorded with the literal sense in about 1440 (when it was spelled hoggyswasch - what a great word!), and the figurative meaning is first seen in the written record in 1712.
I only heard it called slop, or pig slop. It also became a verb: slopping the pigs. 'Most all table scraps went into the slop bucket, which at feeding time had a little milk and a lot of water added. One thing the pigs didn't get were watermelon rinds; they were tossed over the barb-wire fence into the cow pasture--after the seed-spitting contests were over, of course! Mercy, those were some good times! I remember it being hot in the summers, but I was having too much fun to care. Now I'm old and decrepit, and I miss out on all kinds of things because I think I'll get hot. Sigh.