Rats in Plumbing
Rats are surprisingly good swimmers, and combine swimming skills with climbing skills to navigate sewers and water pipes with ease. Their task is much easier in cities with very old sewage systems made of brick, or with combination sewer systems. Combination sewer systems allow rats to access household plumbing from storm drains at the street level.
Older Cities and Rats in Sewers
Older cities like Washington D.C. will have combination sewer systems mentioned above that allow rats to enter your home from the street. Contrary to popular belief, the pipes below your toilet that lead into the sewer are not filled with water all of the time. In most cases, water is only let into those pipes as the toilet flushes. If the walls of this pipe are rough enough for a rat to latch onto, it will climb its way into the bottom of the toilet, through the p-trap, and into the bowl.
Modern Buildings and Rat Prevention
Buildings completed in the past 50 years will most likely have safeguards against rats if the sewer system is old and allows rats to travel into sink and toilet outflow pipes. Such safeguards include rat baffles, which are essentially one-way doors, and smooth-sided piping with a wide diameter. Wide diameter pipes without rough surfaces to grip prevent rats from making the long climb up from the sewer outflow and into the sewer pipe for your home.
What to Do About Rats in Your Toilet
The best way to deal with a rat in your toilet is to kill it quickly. Flushing it will only keep it away for a short time. Most rats are determined and will try again until they are able to enter the home or are killed. An easy and relatively humane way to do so is to pour a cup of bleach into the bowl of the toilet, close the lid and cover it with an old towel. The gas released by the bleach will cause the rat to suffocate and die with about 15 minutes or so. Then proceed to dispose of the rat according to any local laws for animal carcass disposal.