In my basement laundry room is (to my knowledge) the only drain pipe in the whole basement, which hooks into the end of the main line as it exits the house and heads to the septic tank. When we moved in a year ago the drain was loosely plugged by an expanding ring cap. Never having owned a house before I didn't think much of it, but soon enough I learned what it was and why it was there, when a liter or so of black sludge backed up and forced the cap off and nearly ruined the carpet outside the room. Needless to say the smell was horrid. We cleaned it up as best we could and I snaked it five times (and two more from a toilet downstream [installed right onto the main drain line]), but nothing was draining, so we called a plumber.

The plumber took a much larger snake to it and eventually got it flowing again (after ripping out the toilet and snaking it from both directions) but couldn't identify the source of the clog. Meanwhile all the material that was coming up looked like mostly-decomposed food (though nothing we actually eat strangely enough) mixed with the sludge. We also noticed that running any water in the house except the aforementioned toilet caused the sludge level to rise in the drain.

Now the kicker - despite flushing the drain out with buckets of water every few days, a year later it has happened again. We took the same actions to clear it up, but still have no idea what the source is or how to fix it.

The drain itself smells awful, and has since day one (they had it masked with an air freshener when we moved in) so I'm sure it's an ongoing problem, but I'm clueless how to fix it without literally ripping up the basement to replace the pipe.

Can anyone offer advice on how to solve this issue or at least theorize on what the cause is?

4 Answers 4


The plumber you had out kind of left you hanging. He should have put a camera down there to give you more details on what is going on.

Basically your septic tank is backing up or you have an issue with the main line. It could be slight collapsed or pinched or have roots growing in it or whatever.

So your first step is to have someone come out with a camera to tell you what the issue is. For something ongoing though like this I am guessing you have a pretty big job so brace for the worst. From your symptoms I am going to guess you have an old clay main line that is broken/collapsed. To replace this it involved a lot of jackhammering, digging and moving concrete.

  • That's what I was afraid of. I don't think it's a collapse or root though because the snake never runs into anything substantial, the plumber said we would definitely hear it if it were chewing through a solid blockage. We do however know it's not the septic because when he ripped out the toilet (stuck right on the main line when the previous owners finished the basement) the whole line was clear at that point.
    – thanby
    Jun 10, 2014 at 19:53
  • 1
    You have three components of your main line. The part in your yard, the part within a few feet of your house to your house, and the part under your house. It is that second part that is a pain in the butt because you are digging up so much right next to foundation. If it is just part under your house - which I think you are explaining it that way - it is a lot of labor but really not the worst thing, unless your basement has tile.
    – DMoore
    Jun 10, 2014 at 19:58
  • Yeah, the final segment of it under the house before it hits the yard (which we saw when removing the toilet) was clear while the drain was still clogged, which leads me to believe it's just that branch line going to the drain that is a problem. I think I'll just suck it up and have them run a camera through it. As a side note, the previous owner did give me a cryptic warning about needing a lint trap on the washer (which I didn't end up doing because that would require climbing over the washer every time we run it), could it have to do with that?
    – thanby
    Jun 11, 2014 at 12:07
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    Jackhammering your basement is really a DIY job. I think the hardest part is knowing where to jackhammer. When I run across issues like this I usually jackhammer, move dirt, dispose of concrete, and then call out plumber for a quick call. Something like this is usually $200-300 maybe cheaper if you know someone. Then add back rock (buy a few bags), dirt (might need more), and then pour concrete over.
    – DMoore
    Jun 11, 2014 at 14:44
  • The branch runs under at least one wall and a set of stairs, probably another wall before it meets the main line, does that change whether or not it's a DIY job?
    – thanby
    Jun 11, 2014 at 16:15

Turn off the water and dry the area where water is leaking out. Use some of the blue pvc cement made for plumbers. It's seals plastics/rubbers together well enough support over 200 psi. I had to use it plenty of times for my hydroponics setup for leaks. I use Rain-R-Shine PVC cement...just wear a mask, it's extremely volatile, but it's workable in 15 minutes, fully cured in 2 hours. Also, don't be afraid to use a wrench to get the can open...ours always seals itself closed.

  • I'm not sure what you're suggesting the OP apply the glue to. It seems to be a clog problem, not a leaking pipe problem.
    – FreeMan
    Mar 11, 2016 at 16:42

After a plumber cleans the line very well, run some water and verify it flows well. After running water for a few minutes shut it off and see if the water remains in the pipe. I have a hunch that your main line does not have enough slope to efficiently flush particles from the line.


try muriatic acid but be careful

  • 2
    Please explain how to use the muriatic acid.
    – Niall C.
    Apr 11, 2015 at 19:38

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