The siloxanes are coming from almost anything that can clean as well as makeup. Any shampoo, conditioner, body wash, most shaving creams, toothpaste, etc contain siloxanes in one regard or another. Anything that goes down the drain ends up at your local wastewater plant, not just the poo. You should see what they do…

Already being done at a few wastewater facilities and landfills across the nation.
http://biocng.us/

It’s not so much the sulfur compounds that causes damage to items designed for biogas, it’s the siloxanes that kill everything.