A classic example of rat behavior in confined spaces can be found in the Portland, Oregon sewer system, which connects directly to your home. Before the city invested in a separate storm water system, all sources of water, including street runoff from the heavy rains, ended up in the sewer system. Consequently, the sanitary sewers were flooded by rain on a regular basis. The resident Norway rat populations had to run or swim for their lives during these rain events, could be seen erupting from the sewers wherever they could.

Some of the rats would be caught by the floods away from an opening, and they would be forced to run up the side sewer lines that connected to toilets in houses. If the rat in the toilet line was sick or young, bigger rats would enter behind them and cut off their path of retreat. The first rat then had a choice. He could either turn and fight, or take a chance and swim up, and through, the water trap in your toilet and end up doing circles in your toilet bowl. If the lid was down, the rat would swim back the way he came and the homeowner would be none the wiser. If the toilet lid was up, the rat would sometimes be able to leap out. A rat that enters your home this way has no back door to leave by. These rodents are easy to catch, but it can be a long time before you know they are there. Be very suspicious of unexplained water on the floor around your toilet.

Basement toilets sometimes go unused for months and even years. The water in the toilet’s water trap dries out, and there is no longer a barrier to the sewer system. This can allow odors and gasses to enter your basement and even cause an invasion of drain flies or other insects.

A tip from Crawl Space Portland: Flush your down stairs toilet and always keep the lid down. And while you are at it, put something heavy on the closed lid.

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