Residental sewage. I'm glad the system works as well as it does.

August 31, 2005 3:40 PM

How do residentual sewers work? My neighbourhood is perfectly flat. I'd assume that pumps must be used, but A) I have never seen them and wouldn't they occasionally fail leading to ewww? And what about houses that are below the level of the street where assumably the sewer lines are located. How does the sewage get up to the street level sewage mains?
posted by Keith Talent to grab bag (7 comments total)

Drain plumbing generally requires a 2% slope, or fall; which means two vertical feet for every 100 horizontal feet. It's been my experience that the City engineers generally know what they're doing when they install the sewer lines and just install them deeper in certain areas (such as where the living space is well below the roadway). They most definitely do not (again, in my experience) just install sewer lines at a given distance below the street universally.

In instances where we've built basements where the City engineers apparently didn't allow for them, we've had to install sump pumps, which definitely run a risk of "eww". From the City's point of view, if you build low enough that sewage doesn't naturally flow into your sewer lateral that's your problem, not theirs.
posted by LionIndex at 3:56 PM on August 31, 2005

Also, the slope required goes down as the diameter of the pipe goes up. A 12" pipe only need 3" of slope over a 100 feet; a 24" pipe only 1". So you can go pretty far without having to go that deep.
posted by smackfu at 4:02 PM on August 31, 2005

Also, there are locations in my area where there are pump stations. It just depends.
posted by LionIndex at 4:13 PM on August 31, 2005

There is information on How Stuff Works: Sewer and Septic Systems. Specifically, page three.
posted by sbutler at 4:28 PM on August 31, 2005

How does the sewage get up to the street level sewage mains? The specific tool used in cases like that is called a "grinder pump." I'm actually looking into getting one to flow to an uphill septic tank, but it's used for sewer lines as well.
posted by Alt F4 at 4:35 PM on August 31, 2005

I live in an area that has such a pump. Every time the power fails the town highway department is there with a generator to keep the pump operating. During the two ice storms we've had, they were there close to a week each time.
posted by tommasz at 6:07 PM on August 31, 2005

Thanks.

And how I missed the answer on "How Stuff Works" highlights my lax attitude towards research, a problem that many of my high school teachers would confirm. Thanks again.
posted by Keith Talent at 8:18 PM on August 31, 2005