Yep, a rat can come up your toilet. A rat’s ribs are hinged at the spine, enabling it to easily squeeze through the tightest spaces—like the pipes draining your toilet. And rats are great swimmers too; they can hold their breath for up to three minutes. Sewer rats can occasionally find their way into pipes that lead up into toilets. The U-bend of a toilet creates a tiny pocket of air that gives the rat a chance to catch its breath and make its way through that last foot or so of piping, and into the toilet bowl.
See how quickly a rat can go from the city streets to your bathroom.