What Is A Building Sewer?

A building sewer is the pipe that connects a building’s plumbing system to the main sanitary sewer. Building sewers are also called “service laterals”, “house laterals” or “sewer laterals”.

The main sanitary sewer is usually located under the street and collects wastewater, called sewage, from building sewers and conveys it to the wastewater treatment plant.

Why Do Building Sewers Need Maintenance?

Blockages in your building sewer can cause backups of sewage from your building’s toilets, showers and floor drains. These types of blockages are sometimes referred to as “basement backups”. A backup of sewage can lead to disease, destruction of valuables, damage to your property and electrical malfunctions.

Rubbish and other objects put into a drain can combine with hair, grease and other debris to cause clogging of the sewer system. Something as small as a cotton tip swab can catch other debris to create a blockage. Cracked building sewers allow groundwater to enter the sewage system, which can also cause a basement backup.

What Are Sewer Cleanouts?

Building sewers often have cleanouts which provide an access point into the building sewer for cleaning and repair. One cleanout is located immediately inside the building or just outside the building wall. There may be additional cleanouts between the building wall and the main sewer or inside your building in places such as the basement. The cleanout is usually a small pipe about 4 inches in diameter within a frost sleeve (if outside). There should be a cap on the cleanout.

What Problems Should I Look For?

  • Wastewater backups inside the building
  • Slow draining sinks and toilets
  • Wet or soggy ground in your yard
  • Water leaking from cleanouts, outside drains or main sewer manhole covers
  • Unusual odors or sewage smells in or around the building or home

If you suspect that you have a blockage or problem in your building sewer, call a professionally licensed plumber for an inspection. Even if you are not experiencing drain or sewer problems, periodic inspections and cleaning by a professionally licensed plumber is a good idea. Building sewers are usually neglected by the homeowner until problems arise. Simple maintenance such as checking your sump pump and timely repairs can avoid sewage backups and damage to your property and personal belongings.

How Can I Prevent Problems?

Follow these DOs and DON’Ts to prevent problems with your building sewer:


  • Place paper towels, feminine products, disposable diapers, dental floss, hypodermic needles, plastics and other personal hygiene products in a wastebasket. Dispose as garbage.
  • Use sink and shower drain strainers. Clean them out regularly.
  • Collect grease and fats in a heat-resistant container. After it is cool, dispose of it in your garbage with solid waste.
  • Compost food scraps or dispose of them in your garbage with solid waste.


  • Don’t use the sewer as a convenient means to dispose of food scraps.
  • Don’t use the toilet as a wastebasket for garbage, medications or chemicals.
  • Don’t plant trees or large shrubs near sewer lines where roots can penetrate and form a dense “root ball” blockage.
  • Don’t pour grease, fats or oils from cooking down the drain. Grease in drains collects and hardens into a plug.
  • Don’t connect French drains, roof gutters, sump pumps or other flood control systems to your sanitary system. These types of connections are illegal.

Why Are Infiltration And Inflow Big Problems?

Infiltration and inflow (I/I) are terms referring to groundwater and/or rainwater that enters the sanitary sewer through cracked pipes, leaky manholes, roof and gutter downspouts, sump pumps, foundation drains or improperly connected storm drains. Most infiltration comes from ground water and most inflow comes from rainwater and/or snowmelt. Extensive studies have shown that as much as 40% of I/I enters the collection system from building sewers.

Additional I/I flow in the sanitary sewer collection system results in the need for larger sewers and treatment plants. Higher sewer user fees must be collected to treat the increased volume of wastewater from I/I.

What Can I Do To Prevent And Reduce Infiltration And Inflow?

Make sure the cap to any cleanout is secure and has not been damaged.
Disconnect illegally connected outdoor patio, deck, yard or garage drains that may be connected to the building sewer.
Reroute sump pump discharges illegally connected to the building sewers to outdoor lawn areas or storm drains.
Redirect rain gutters and downspouts illegally connected to the building sewers to rain gardens, lawns or storm drains.

Who Is Responsible For Maintaining And Repairing The Building Sewer?

Property owners are usually responsible for maintaining and repairing building sewers. However, there may be special circumstances when a municipality will pay for the repair and maintenance of all or a portion of the building sewer.

If a building sewer needs maintenance or repair, always call your wastewater utility to verify local requirements. Your wastewater utility may also want to perform an inspection prior to the repair in order to identify if there is a problem with the main sanitary sewer pipe. The installation and maintenance of the building sewer is regulated by the Department of Commerce, Safety and Building Division.


This publication of the Wisconsin Department of Natural Resources and the Wisconsin Department of Commerce is available in alternative format (large print, Braille, audiotape, etc.) upon request. Please call 608. 267.7694 for more information.

Wisconsin Department of Natural Resources
Bureau of Watershed Management
P.O. Box 7921
Madison, WI 53707-7921