Numerous people have reported finding possums in their toilets...
These guys can crawl up the pipes the same way a rat or squirrel can, making rodents the most likely animals to wind up in your toilets.
http://orzzzz.com/top-9-strangest-creatures-that-might-show-up-in-your-toilet.html
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A Possum is a *Marsupial*, not a rodent. It has a pouch for its young like a Kangaroo.
We humans say, “don’t tread on me”...
Meanwhile, that creature’s facial expression says “don’t crap on me”