I excavated a wall in the corner of my basement and found what I'm assuming is a drain pipe, but the location has me baffled. It's literally in the corner of my basement. The placement doesn't seem ideal for a shower, sink, or toilet and there is a bathroom just 15 feet away.

Oddly, there's a 20 amp duplex outlet installed in conduit right next to a 15 amp outlet that was just nailed to a stud.

Could this be part of a french drain or something else related to a sump? I don't see any signs of a post pour addition of a french drain.

If the picture I'm attaching works, it's either a 4 or 5 inch pipe that's capped.


I noticed a crack in the pvc, so I started excavating to repair it, whatever it is. Inside is a smaller piece of corrugated pipe, maybe 2 inches across. It looks like it's wet. The part of the elbow that's under the concrete doesn't seem to have any pvc leading from it.

Does this help identify what I have here?

New picture: enter image description here

  • 1
    Could well be a "just in case" radon vent system that was not needed, so it was capped. Cheaper to put it in before pouring the foundatin and find it's not needed than add it later if it was.
    – Ecnerwal
    Dec 11, 2015 at 0:28

2 Answers 2


It actually isn't that bad of a place.

  • Most basement bathrooms I do end up being in a corner.

  • Builder planning on actual drain location is basically useless because they can't get in your head on what you will want in 5 years.

  • Remember that what you are currently seeing will be covered.

  • The corner location allows you to easily connect your sink drain without busting up more concrete for that. So you will bust up the concrete around this and connect your toilet and shower to a point where you have an acceptable pitch for each. Toilet will need to be relatively close and shower can be further away. Given that it is in the corner I can throw an adapter on the top of this and run the venting and the drain from sink through the walls. If this was in the middle of the room you would have an extra line that you would have to connect below grade for sure.

  • Given this configuration and a "normalish" bathroom you could bust up concrete with just sledge hammer and have toilet, shower, and sink lines completed in a couple hours. After it gets inspected you could have this concreted the same day if you can line up your inspector right and if he trusts that you will have it completed (you would have cut the top off and framed beforehand if you want it done quicker).

So really if I am doing a bathroom this is a great place.

Edit: Since the OP added that they are installing a french drain on the perimeter my advice would to leave this in tact and work around it. There is no reason this should really affect a french drain system.

  • That makes sense. Thanks for your thorough response!
    – thatguy
    Dec 11, 2015 at 1:54

It's possible that this was installed as part of a Radon mitigation system, or for future use as part of a Radon mitigation system if one was needed.

You shouldn't use it as a drain, unless you've verified that it ties into the main plumbing stack. Since you probably don't want to dump sewage under your slab.

  • Thanks Tester101. They installed a bathroom in the basement already, so I don't plan to touch this. I am considering installing an interior french drain and I was curious/hoping this was a preplan for that.
    – thatguy
    Dec 11, 2015 at 16:29
  • 1
    It could also be a cleanout, or connection point for a perimeter drain system. How old is the home? Is it possible that there's already a perimeter drain system installed?
    – Tester101
    Dec 11, 2015 at 16:53
  • It's around 20 years old. The gutters are piped in to pipes that drain to the municipal storm sewer. The top of the cap in the photo is about 7 feet below ground level on the other side of that wall. I'd be very happy if a perimeter drain were already in place. The 20 amp outlet nearby has always made me wonder what else they originally had in the room. The cap doesn't unscrew, making me think it isn't a clean-out. Is there any information that would help determine with certainty what it is, if it's not a drain?
    – thatguy
    Dec 11, 2015 at 20:58

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