It is not unusual for us to find that failures in the sewer lines have caused a rat invasion in a crawl space. The sewer line that connects to your house enters the crawl space or basement, and can fail in several ways. Old age combined with tree roots, soil settling, and heavy machinery, or just an automobile driving over the lines, can damage a sewer line enough to encourage rats to tunnel out from the break and follow the line back to the house foundation. Look for smooth round tennis ball size holes going straight down. Do Not Fill these holes with anything that you dont want in your main sewer line.
During our initial inspection and evaluation, we always look at the place where the sewer line enters your foundation. These entry holes are almost always larger than the sewer pipe itself. Rats that tunnel along the soft underside of an old damaged pipe will find and use these openings either to get in, or as a back door, to get out. A broken sewer line will still function for a while, but rat activity in the break will eventually cause the system to back up into the house.
When we find a sewer cleanout cap sticking up from the ground next to the foundation, we take a closer look. Rats love to dig around these pipes because the dirt is soft and they smell interesting. If they dig far enough, they will find the oversized sewer line hole in the foundation, or just dig under a shallow footing, and come right in.
In the older parts of Portland there are crawl spaces with open, unplugged, abandoned sewer lines that still connect to the main line under the street. These eighty to one-hundred-year old sewer lines can be left uncapped, or buried without a cap right next to foundations and basement walls. These rat highways are usually missed by other pest control companies. These abandoned lines are often the source of the smooth holes that appear in the middle of a front lawn or flower bed. Do not try to fill these holes up with dirt or gravel, You are just making the problem worse.
We are Sewer Rat experts so call us right away if you see any smooth holes with no dirt around them, or places where your lawn is settling for no apparent reason. 503-579-3680