I can assure you I (we) know what "dirty" is and would be happy to give you more detail if you desire. We raise some of our own food now (though we both grew up on ranches/farms that did even more). We are familiar with the gamut of techniques for raising food, from primitive (I've plowed a field with a plow attached to a horse) to modern (it's much easier with a tractor, and while modern, a manure spreader is only easier to use, not a lot cleaner). Night soils are for use when you have no other option and night soils from people with contagious diseases are NEVER to be used (and you have NO IDEA if some random toilet in some random house had someone with a Z plague use it before they started looking for brains).
Yeah, I was talking about The Martian. Why would you assume otherwise?
EDIT: The point being he was aware of where the poop/♥♥♥♥/turds came from and that they would be from healthy people (since presumably they screened for such things before they sent them to Mars), not some random toilet. And it was a great reference, The Martian was a great movie showing low-tech techniques in a high-tech environment, among the MANY other great things about it.