I read a story a while back from some guy that was a mechanic for American Airlines I think and he had to work on a plane's toilet system. It wasn't his job but the usual toilet guy was out sick or something. So he goes into the bowels of the airplane to work on the toilet system and he found all kinds of extra plumbing throughout the airframe, tanks and sprayers and parallel lines. He did his work and then buttoned everything back up and went on his way. A couple of days later he got called into the office, and was questioned by a couple of suits, told to forget what he saw and keep it to himself. He retired soon after, but says it freaked him out.
I'll see if I can find it. Had some pictures if I recall.