Define sewer?

A sewer is a system of underground pipes and channels used to carry away sewage and wastewater from buildings to a treatment facility or disposal site.

A sewer is a closed, often underground, waterway designed to carry waste water and sewage away from homes, businesses, and other buildings. Sewers are typically made of concrete or plastic pipes that are laid underground and connect to a nearby treatment plant where the waste water is cleaned and treated before being released back into the environment.