They make rubber drain plugs for this very purpose. Found in the plumbing dept

If its PVC, a standard 4" cap will work, attach with pvc cement, otherwise the rubber cap mentioned (fernco) attached with worm clamp.

I wouldn't cap a drain pipe until I was certain I could. What was its purpose? Is it abandoned?

A cap with cement or a test plug. The test plus is a rubber stopper that uses a screw mechanism to squish it. As is squishes outward it seals into the pipe giving a great seal. I've used one on an unused DWV and another on an old toilet flange. Ask at any hardware store and they'll have it.

"...We've got a 4" underground drain pipe that we uncovered as we were digging our room addition foundation. It comes from under a patio slab, and presumably originates uphill in the nether regions of the back yard somewhere. We have no idea where, as there's no visible inlet.

If we don't block the flow, it will continue to deposit water around the foundation. Can we just clog up the end of the pipe? If so, with what? Any other recommendations on how to deal with this?..." - weedy acres

This is a drain pipe. Required in most places to let water that comes near your home a way out. If the pipe is solid it could be the tail end of your rain water leaders from your gutters. Do not plug the drain line! That would be insane.

Call the city and find out where your storm and sewer line connections are. You should be able to find two 4" caps at the opposite side of your home. These are clean outs.

New construction will see these lines enter a sump and then out to a city connection. If you run water down the gutter waste line you should hear the sound of water running through these lines.

The addition will require more drainage as well. The top of the 4" pipe needs to be lower than the bottom of the basement concrete slab.

"Originates in the backyard somewhere" Doesnt sound like a weeping system to me. If anything it would bring water towards the house.

It's an asbestos cement pipe, not PVC or even corrugated plastic. Old, like the 100-year-old house. This pipe definitely doesn't connect to any gutter coming off the house, and the only thing upstream from it (following the direction it came from) is back yard. Based on the direction it's going to, it ties into the sewer line.

In the far reaches of the back yard there are some relics of a structure that used to be there (some concrete blocks, a gas line and a water line that traced back). So best guess would be that this was a drain pipe in that structure. But no inlets for any of these lines, so no way to verify.

I am highly confident this drain is not draining anything away from the house. It is currently draining something right up to our new room addition foundation, and not below the basement level. So something needs to be done about it. But I don't know if plugging it up will cause unintended consequences elsewhere.

I'd dig that thing up until it was at lease 25 feet from the house. If the plug or pipe lets go in the yard, big deal, you've got a little extra landscaping to do.

Old sewer lines where Asbestos and about 4" inside dimension. Could it be a sewer line? Can you call the city and ask for the info on your home? They might show the old sewer line.

My home was built in the 50's or 60's it also had a sewer line made from Asbestos. I nicked it when building my garage and repaired the line with ABS pipe.

Is the pipe cracked or exposed anywhere?

Here's a diagram that might help show where this new pipe is relative to the house and lot.

The only exposed parts are the yellow on the left, and we exposed them when we dug the footers for the addition. We removed the center of that yellow thing to pour concrete, so there's just an outlet at the end of the slab and an inlet on the south side that lead to points unknown. Both of those ends are exposed at this point, but nothing else.

Hard to say if the underground portion is cracked or damaged, as we can't see it. :-p

I can try calling the city water dept, but since the power company had no records of the gas line we found running along the same path, it's likely the city doesn't know about the water and sewer.

So it used to be a complete system (possibly) but you hacked into it?

I think I'd want to know where that pipe goes and plug it at the source if it's no longer needed. Hire someone to trace it using a transmitter that they shove up it and then walk over top with the receiver to see where it heads.

I spent several hours and some money "repairing" a section of my septic system that wasn't connected to anything. The previous owner had it redone; I dug up the old one when planting large trees and panicked.

What happens when you flush the toilets now? What happens when you dump a full bathtub of water down the drain? These are basic simple checks. I would be filling the tub and letting it empty over and over - at least 4-5 times.

greg: Yes, this appears to be a line that we hacked into. Interesting idea on how to trace its origin.

joe: did you repair it (i.e., put it back together) or remove/plug it up?

john: 100% of our household sewage goes out a drainpipe in the corner of our house marked "main sewer line" in the drawing above. We know this because it's all visible from the basement and because Mr. Weedy personally ripped out and redid all the plumbing in the entire house. We also know that that sewer line feeds into the street (not upstream to where that other pipe is) because we had a clog 6 months ago, snaked it out, called out the water company, etc.

I did call the public works department and left a message. No return call yet.

If this pipe is fairly near the surface in your back yard, then I suppose my question may be clearly of no concern. However, what is behind your back yard? One hundred years ago, your neighbor could have had an easement thru your yard for their sewer line. Even if new sewers run to different streets, old lines could run to first laid sewers.

In the house we just bought, there is an underground drain that originates in our yard, continues under the fence, under the downhill neighbor's yard and flows out to the street. It's a problem for us that it appears to be partially blocked somewhere under the neighbor's yard. Any possibility that your uphill neighbor is at the other end of your pipe?

Interesting hypothesis about it being a neighbor's sewer line. Fortunately, behind us is just a ravine, no neighbor. And I suppose if it was someone else's sewer, we would have seen something other than a trickle of water coming out of it the 2 weeks it has been exposed.

Since we're going to put drainage around the new foundation, we decided we'll just Tee the incoming pipe into the new one somehow. Not sure how you connect asbestos and PVC pipe. :-/

Fernco couplings

However, I personally would not tie it into your weeping system, you want water to be directed out of the system, not into it. I still think your original idea of capping is ideal. You never saw or smelt sewage and there is no chance it is a neighbors or a city sewer line, so its an abandoned pipe in the ground as you thought.

Actually, I wasn't suggesting a sewer line. The one of concern to us is just a water runoff pipe that directs rain water somewhere other than under the house. If what you have behind your house is a ravine, then I think you can cross that possibility off your list.

Your yard runs _uphill_ to a ravine? Is it a very high ravine? LOL
If the vanished building in back was part of your property, maybe the line was laid to collect its gutter runoff and bring it to your house's cistern. People used to be extremely keen on collecting rainwater. One large local house I know had 3 cisterns of its own, and 3 more at outbuildings including the formal gardens.

LOL Casey, the yard runs uphill, then past our property line goes downhill into a ravine. We get lots of city deer running through our yard.

Cisterns are an interesting hypothesis. I'm not keen on digging up the yard to prove it, though. ;-)

Weedy, when I saw your thread title, my mind went to "how to best clog up a toilet". While several possibilities came to mind, I couldn't imagine why you would want to! Then I hoped perhaps it was a funny story about toilet clogging, but no.

I hope your problem has a satisfactory resolution.

The city water/sewer guy finally called me back. They've got no record of anything, and he suggested some of the things you guys have: is it from our roof, from the neighbor, etc. So no help there.