Why is there pooling in an undamaged drain?

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    • #279271
      Corky Akins

      I bought a 150 year old building in December last. The drain runs from the back of the building under the building out to the front.

      In February, it got blocked and I had it cleared. It blocked again in March and has just blocked again in July.

      So I got a camera down. There appears to be no damage to the drain, but there is a pool of water in the middle of it. The camera guys weren’t able to explain it but said I might need new drains. I am reluctant to dig up the floor of a house without knowing exactly what the problem is.

      I checked with the previous owners and the people to whom the house was rented and there is no history of blocked drains.

      I just can’t understand how it could happen fairly suddenly?



    • #300416
      Retired plbg1

      Sounds like pipe might have settled in that spot. Next time it stopped up have camera run in and see if thats where it is stopped up.

    • #300417

      Thanks for the quick reply.

      That’s where the blockage is ok, but what I don’t understand is why it should have settled so suddenly or so recently.

      Is the only cure to replace it? What about inserting a pipe within the pipe?


    • #300418


      RP’s suggestion that the drain pipe has settled appears to be correct…it would explain why the water pools in that area. A sag in a run of drain pipe laid in soil under a slab (or elsewhere) is not unheard of.

      The question is whether you need to do anything about it.

      If there is nothing else wrong (such as leaks or sagging so severe it leads to obstructions to flow in the pipe), there is no reason to do anything. In effect, the pooled water may present as nothing more than an “unintended trap” in the drain line…in effect the equivalent of a building drain “u-trap.” The problem is, however, that solid waste may hang up in this “unintended trap” and may need to be snaked out. Unlike an intended u-trap, your sagged pipe run is not equipped with clean-out plugs…


    • #300419

      Thanks Nick

      It’s got blocked up 3 times so far this year, so I presume that I have to do something about it.


    • #300420

      The fact that it’s blocked three times means that you need to replace the line. It may have been OK for 150 years, but something made the line sag too much recently. Maybe there is a leak that has eroded the soil under the pipe. That would be another reason to replace the sewer.

      If you have a concrete slab under the building, and you want to run the replacement line in the same location, you will have a major and costly demolition job. This is the time to consider rerouting the sewer along the outside of the house. Both options are going to be costly, but there may be a signifant savings with one versus the other. Your experience illustrates why I dislike running pipes under slabs if there is another way to do it.


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