Like shit and piss anon. A very strong outhouse odor. Ammonnia city.
If anyone remembers that "expose" on the greys going around a few years ago, part of the anatomy thing is that they do not shit or piss. Waste is processed by internal organs and the sent to the skin to be sweated out.
I thought that was bullshit years ago but once you meet several "people" with that shape and smell ya figure it out. No secret at all if you have them in your neck of the woods.