We used to use that lye shit in McDonalds, back in my youth to clean all the oven trays, all the fryer parts and all that. Used to fill up a sink full of hot water, sprinkle in a couple of packets of that shit, and let it soak for a few hours, it was called burnout. The stuff would eat away all that oil and gunk that turned into a varnish over time. Its probably whats in oven cleaner too but at a lower concentration.
Wasnt there some biker gang in Canada that used to do just that? They would kill prostitutes, run them through a wood chipper or some shit and let the pigs eat the slop. They would of never found out either, it was by chance they caught these fuckers. And, yes, they did find bone fragments all over the place.