The other day, I was doing some digging at the side of my house, and
found something that I have no clue what it is or what it is for.
I was digging near the area where the sewer pipe exits the house. I
always assumed that the lateral is just a simple sloped pipe that heads
out to the municipal street sewer. However, after the lateral exits the
house for a few feet, it inlets into a little dry-well type structure
that is about 2 ft in diameter and covered with a round stone slab.
Then, there is an outlet on the other side of the dry-well that acts as
the continuation of the lateral. The house is about a hundred years
old, and so this must have been part of the old sewer system, but I'm
not sure what the purpose of that well-structure is.
Any ideas? I have some ideas on what it might be but I don't want to
answer my own questions and just have people repeat it back to me. I
want to hear what a professional plumber would say or someone else
knowledgeable on the subject would say.
Thanks for any help provided.
I worked with plumbing for quite a few years before I retired. I did
not do all that much underground work but I worked on a few sewer
lines. I never saw anything like what you describe. Every one I ever
saw was just a pipe going to the street which was normally clay on
older houses. The only thing I can think of, would be a grease trap.
However, those were normally only on septic systems. Of course, there
probably was a septic 100 years ago, so what you have might be a
manhole of sorts where they converted the old pipes from the septic to
the city sewer. Then too, assuming you are at your foundation level,
which means at least 6 feet deep, there would be little sense in
having a grease trap that deep.
It would be much easier to ID if you posted a photo. Got any way to
Also, tell us this......
How deep it it?
What material is it made from?
What state and / or country are you in?
What material is the lateral made from?
If you lift the rock, can you see sewerage flowing, or is this thing
Are there additional pipe inlet /outlets, such as where rain gutter
drops could have entered?
Is this "rock" a plain field rock or a cement casting?
Is there gravel around it?
Are there any drain tiles nearby?
Are there "drops" (pipes) under your downspouts?
If yes, where do they go?
Why are you digging anyhow?
*** Is is filled with money? <lol>
From: Speedy Jim
It used to be common practice (still is in some places)
to provide a "house trap" on the lateral leaving the bldg.
It could also be a "backwater valve" to prevent sewage backing
up into the house; kind of a check valve.
total depth from ground level (the lid is a few inches underground) to
bottom is about 4 feet. There is the cover, then the well goes down 2
ft, then there is the inlet hole for the lateral on one side and the
outlet hole for the lateral on the other side, and then the well
continues down another 2 ft.
Clay... shape-wise, it's very similar to those plastic buckets that
sump-pumps sit in. It has a bottom, the a clay wall about 4 ft tall, 2
ft diameter, and then it flanges wider at the top.
It is being used... the bottom 2 ft (as previously described) is filled
with sludge, and the top 2 ft is clear... I imagine this is a direct
result of the design, since the inlet and outlet pipes are at the
No... I saw on a website that some old city houses and buildings had a
drywell for rainwater from the gutters to flow into and dissipate
through holes (kind of like a seepage pit used further out from some
modern septic tanks)... but there is no connection to collect any such
water... there is only the inlet which is the sewer pipe coming out of
the basement, and the outlet which I'm pretty sure goes to the street
The cover? It looks like a limestone slab... 2 ft diameter, 3 inch
thick. It's round and covers the clay-well, but it's not a great
seal... I think a previous homeowner brought it in when an older cover
was perhaps broken.
Some driveway gravel, but not a special gravel section to suggest
drainage if there were holes in the well.
Nope... I covered part of this answer a few questions back.
I need a good bed of limestone in the driveway before paving on top of
There might be a Lincoldn Wheat Cent or two at the bottom of the
OK, I get a much better picture now.
That seems like an awfully shallow sewer pipe for the cold winters of
Michigan. Being that shallow tells me that it originally went to a
septic. Modern sewer pipes are generally below the basement floor and
go deeper outside.
I would say that it's most likely a sediment separator and/or grease
trap. They did things quite differently in the old days. Grease
traps were used to keep heavy grease out of the septic, which tends to
clog with greases.
In many ways, it sounds real handy, because if your sewer backs up,
you can access it for cleaning easily, and if the sewer system backs
up, you can prevent the house from filling with sewerage by opening
that thing. Plus if you flush your wedding ring down the toilet, you
know where to find it (yuck).
On the downside, if no one knew it exists, the poor plumber that would
try to run a rotary auger from the house to the street, would be
really frustrated when the auger kept stopping at that point.
I would highly recommend that you DO NOT pave over it. Make yourself a
nice concrete cover or buy one. In the future there WILL come a time
you'll need to get in there. I hope this is not being driven over.
Walking is fine.
It might be interesting what sort of objects are in the bottom of that
Well... I have two issues with it that makes me not want to just let it
1) I worry about a future service call not being able to send a router
cable through the system... this will not be a problem if I discontinue
the well and connect the two pipes (the inlet and outlet pipe).
2) I have to pave over that area.
If it's a grease trap, I can't imagine one house producing that much
grease so as to be a problem. If it's some sort of of back-up valve,
the sediment has filled up to the pipes, and so I don't see how it
would accept much backed-up water before sending it on into the house
anyways... however... in case it still has some value as an access
point for roto-cabling further down the line, or as a water-back-up
tank... I might simply take out the tank, and instal a "clean-out" tap
a few feet closer to the house so as to avoid paving over it... the
only question is, I don't know if a clean-out access tap can have a cap
that allows back-up to flow out (sort of like a pressure release
valve), and thus avoid backing up into the house.
Though to be honest, I wish I knew exactly what the thing was.
In a 1961 (copyrighted date) version of Popular Mechanics Home Handyman book
series, there is a picture of what you describe. Made out of vitrified clay
or concrete. It is described as a grease trap and it says it was usually
only a necessity on farms where a large amount of meat was processed. I
assume they mean the farm processed its own pork and beef, etc instead of
buying meat already butchered and cut up from the market. It also says that
some states and localities also required them. It further says you should
not have one of these if you have a garbage disposer but should enlarge the
septic tank by 50% instead. It doesn't say anything about maintenance but I
would assume the farmer opened the top and cleaned it out regularly. It
shows it as being 36" deep and 24" across with the house line coming into it
12" from the top and the outlet line designed so it picks up the outgoing
liquid about 6" or so from the bottom and then up and out 12" from the top.
It calls for a 2" min. line and altho it doesn't actually show where in the
sewage line, it goes, I can't help but believe it is designed to be in a
separate line from the kichen and then meets up with the bathroom lines that
would transport solids, somewhere outside, before ending up in the septic
tank. Its design doesn't look like it would allow solids to pass through
it. Of course it may have been a design used before the advent of indoor
I checked to see when municipal records say the house was built, and it
was in 1920. It is in the "downtown" area of our city, so it's hard for
me to guess whether there was any sort of city sewer line there at the
time. If there wasn't, I'm contemplating the well as possibly part of
an older mini-septic-system of some sort... If there was city sewer,
then I'm viewing the well as some sort or pre-treater where the food
and stuff had a chance to break down some before sending it on to the
I'll check the local libraries for that old issue of PM and see how
similar it is to the item in question.
On Sun, 13 Aug 2006, firstname.lastname@example.org wrote:
The oldest houses in the downtown area of Madison WI have something
similar. I always took it to be an artifact of the superstition that
people seem to have had in the 19th century with regard to sewers and
sewer gas and the like.
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