Your side sewer is the pipe that leaves your house and connects your waste drainage to the sewer system. The pipe must be vented so that air can enter the side sewer and allow drainage to occur properly. The sewer pipe is NOT the same as the rain run-off drainage system. They are not connected to each other except in very old systems.
As long as your side sewer does not become blocked your waste materials should flow out of the house and into the sewer system without problem.
In some cases that side sewer can become blocked. This usually occurs due to structural failure of the pipe or intrusion of the pipe by vegetation. Older pipes might fail on their own due to age. Other pipes may collapse due to heavy equipment running over them, especially if you have construction work being done on your home or yard.
Trees can intrude on your pipe and block it when roots penetrate the pipe and block it. In older neighborhoods like in Edmonds or Everett, sewer repair rates are often higher do to the older established trees.
If a pipe becomes blocked it may need to be replaced. This may be difficult and expensive, especially if the pipe is covered by hard scapes or trees. In some cases, it may sense to replace the pipe with a new pipe in a different location.
In some cases replacing the pipe can be a difficult procedure. In the past gas lines were run to houses using underground boring equipment. At times the gas pipes were drilled directly through a sewer pipe creating what is known as a cross-bore. Removing the cross-bore so the sewer pipe can be replaced adds cost and time.
Just because your sewer is behaving correctly does not mean you do not have any problems. It is good to get a video inspection of your sewer line periodically to detect any developing sewer repair problems early. If you are purchasing an older house in an old neighborhood in North Seattle, Shoreline, or Edmonds. Sewer repair problems could be looming and it is a good idea to get a sewer inspection.