Summary: Believe it or not, the story of the toilet rat is not such an uncommon occurence. Finding their way from the street sewer line into your household plumbing is a fairly simple task for a rat.
It's like the old Psycho shower scene. Nobody wants to think about Norman Bates sneaking into their bathroom while showering, but after you're seen that movie you can't help but think about it.
The same lingering fear holds true for stories about rats coming into toilet bowls while we're sitting there minding our business. However, before you give up the convenience of indoor plumbing and start digging latrine holes in your backyard, please read on.
***image1***How do rats actually get into the toilet? Well, let's assume it did, in fact, come from the inside of the toilet and that it didn't arrive there from other entry points and jump into the toilet looking for a drink. (Rats require water everyday.) One entry point to consider are the vent pipes on the roof. Rats are terrific climbers and jumpers. Placing a vent cap or mesh wire over the vent pipe is not unreasonable especially if you have a lot of over-hanging trees on your property. Rats can easily navigate the trees and jump to your rooftop.
First floor toilets are probably more susceptible to rat invasions than upper level toilets especially if the toilet soil pipe runs horizontally or at a very shallow angle to the sewer. Rats are good underwater swimmers. (They can swim one-half mile in open water and can tread water for up to three days.) It's totally possible for a rat to walk up a horizontal soil pipe from the sewer, swim through the water-filled piping inside the toilet, and surface in the toilet bowl. However, if the soil pipe runs vertically for five or more feet the rat will have difficulty climbing the inside of the slick, wet pipe.
***image3***Most toilets have traps that hold enough water in the connecting pipe to discourage the rats from coming in. However, in unused guest bathrooms and abandoned houses trap water can evaporate.
If a rat actually does happen to get into your toilet, the first thing you should do is shut the lid. They can jump out. With the lid closed, squirt liquid dishwashing soap into the bowl between the opening of the seat and the rim of the toilet. The dishwashing soap makes the bowl and the pipe below it slippery, making it hard for the rat to get any traction. Then flush the toilet. Usually the rat goes down and doesn't come back. Then, call the City and demand that they bait the sewers. Probably wouldn't hurt to call a pest control professional, too.