- Public Works
- Your Sanitary Sewer System
Your Sanitary Sewer System
Your sanitary sewer system (PDF) is very much like your water heater - you don't think about it much until it doesn't work. Sewers are something that are taken for granted - out of sight, out of mind - until the out of sight part stops working.
A basic understanding of the plumbing and sanitary sewer systems in your house will help you to know what to do if waste water does not drain from your house:
- The sanitary sewer system begins with the drains inside your house. All of the drains from the sinks, toilets, etc. are piped to the sewer service line that exits your house underground and connects to the sewer main under the street.
- Each drain has a "trap" that prevents sewer gases and odors from entering the house. Each drain also has a roof vent pipe that exhausts gases through a chimney-like stack and admits fresh air to the drains.
- Vents maintain the pressure behind the flow of drain water and wastes, thus preventing water from being siphoned out of the traps.
Drain Pipes & Vent Pipes
Drain pipes and vent pipes, collectively called the drain-waste vent, or DWV system, must work together to drain water and waste. If a vent pipe is plugged, the drain will burp and bubble as water drains out.
If only one section of plumbing does not drain, it is usually an internal plumbing problem. However, if no drains work or the entire system drains slowly, or the worst case scenario occurs, waste water comes back up through the basement floor drain, the problem is outside of the house in either the sewer service line or the sewer main.
The sewer service line is typically a 4-inch diameter cast iron pipe, plastic in homes built after 1980, and is installed under the basement floor.
A clean-out opening is normally installed at the basement floor line just before the pipe leaves the house.
In case of a blockage in the sewer service line, plumbers use this clean-out opening to eliminate blockages occurring between the house and the sewer main.
The typical length of the sewer service line from the house to the center line of the street, or the sewer main, is 60 feet. The first 30 feet of the sewer service line is typically cast iron, and the remaining 30-foot run to the sewer main is clay pipe.
The Sewer Mains
Most of the city's sewer mains were installed in the late 50s and early 60s.
Much of the system is 8-inch clay pipe that connects to the large Metropolitan Council Environmental Services' interceptors that ultimately convey sewage to the Pigs Eye Treatment Plant in St. Paul.
Our utility department cleans and maintains miles of sanitary sewer mains and several pump stations.