It can usually be found in the basement, garage, or crawl space. You will want to look for a pipe that is about four inches in diameter with a screw cap on the top with a notch or a square knob at the top. Note that some houses have an indoor sewer line cleanout point, while others might be located outdoors.May 29, 2020,
Perhaps the best way to obtain this information is to contact your local water authority, which is also the organization that would be responsible for any problems that may arise with shared drains. Another way to check and see if you have a shared drain is to check with the sewage company that services your area.
Generally speaking, you're usually responsible for drains inside the boundaries of your property, while the sewerage company is responsible for lateral drains, which are usually outside of property boundaries, and sewers. Although most sewers are now publicly owned, there are still some private or unadopted sewers.
For indoor main drains, you will likely find the cleanout in a bathroom or utility area. When dealing with a bathroom location, check the floor near the toilet. In this scenario, it might be a pipe protruding from the floor or it might be flush mounted into the floor. These main drains tend to have a threaded plug.