I'm pretty certain that there isn't a real-world analogue to this little idea. Yet I'll post it and await the responses.
The sewage system of a multi-species space station would have to be one of the most sterile places because it's full of bugs from countless worlds which may or may not have biologies based upon different chiralities, harsh environments and just basically being a stew of alien offal. All this horrible stuff combined would be effectively sterile since one bug would cancel out another bug and so forth.
Doesn't mean the ship's doctor will be washing his tools in this sludge.

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Or maybe it would be one of the most virile. Each bug, in a completely new environment, with many new competitors and predators, all struggling to survive. Who knows what could evolve?

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Please explain your reasoning. Your assumptions are not persuasive to me.

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I think mostly it's the opposite--two bugs, being mutually alien, do not interact, so either planets' inhabitants could be infected by the sewage. On the other hand, if some bug excretes lots and lots of benzine, it may quickly become a monoculture that can poison, if not infect, anything (sort of like the first life forms that produced oxygen basically poisoning the planet).

Actually, a ship with multiple alien species might just need to have multiple separated compartments, or better still, separate ships.

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Todd (Bowie, MD, US, North America, Earth, Sol System, Vega region, Local Bubble, Orion arm, Milky Way Galaxy, Local Group, Virgo A Cluster, Virgo supercluster, the universe in which spock is clean shaven)

Quidquid latine dictum sit, altum sonatur.

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