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Recently we started noticing several issues with drainage in our master bathroom/shower, that resulted in overflow into our downstairs kitchen sink. They look to both be on the same plumbing stack.

We called a couple of plumbers into review and they tried to unclog. One did a full camera inspection and found that the issue causing the blockage, which went back to the sewage line, was due to the sagging pipes under the basement foundation. They said these were not installed properly, which is causing the water to pool in the pipes (sagging area), and that overtime this build up has caused the blockage. They also said the grading was a concern.

The plumbers were surprised that this issue was occurring in a new home. The guidance I got was that the only permanent fix is structural by digging up the basement foundation and flooring under which this pipe runs (around the utility room), and replace these with straight/non-sagging pipes. This will have to be done to the outside sewer line. Otherwise the clogging will return as the sagging pipes will again start building up.

Is this true? Would hydro jetting work as an alternate to snaking (which we tried)? Or do pipes have to be replaced.

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    It's possible, depending on your locality and how big the builder is/was, that he had to pay for a bond to help cover issues like this.
    – SteveSh
    Commented May 30, 2023 at 10:58
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    A builder (or sub) installing a pipe with a belly deserves to be called out for shoddy work.
    – Huesmann
    Commented May 30, 2023 at 12:26
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    Have you had the house for five years, but this problem is recent? Problems with pipe slope(sagging) should have shown up before now(clogs/slow draining) if it was the way the pipes were laid.
    – crip659
    Commented May 30, 2023 at 14:43
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    @crip659, that's not true. Modern pipe is slippery, and the force of even a short water column can push a lot of stuff through without issue. It's only over time that sediments start to bond to the pipe and cause clogging.
    – isherwood
    Commented May 31, 2023 at 13:09
  • Which is a good reason NOT to pour grease down a kitchen drain!
    – SteveSh
    Commented May 31, 2023 at 13:27

1 Answer 1

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Pipes with inverted slope will need to be rectified. There is no other remedy that will last. There are a couple ways to do this:

  • Open the slab (which is not the "foundation"--that's only at the perimeter and maybe key interior locations) and relay the pipes. This obviously can result in the need to tear up and replace finished flooring, but otherwise isn't too traumatic if done by a caring professional, or you. This is very much a DIY project for a person with the ambition. Even the slab repair isn't too difficult.

  • Install an ejector pump. This involves putting a pit in your basement to get the pump below the current piping. It's an extreme measure and probably not appropriate. I only mention it as a possible alternative if the previous strategy is prohibitive for some reason.

If the section of pipe with the inverted slope does pass under the foundation wall or interior footings, this still probably isn't a serious issue. A footing can span a short distance temporarily without collapsing. The pipe can be excavated carefully and repaired.


This sounds like the kind of thing that a builder is responsible for in a new home in most areas. It's not "structural", but it does involve highly regulated sanitation techniques which have health and safety implications. Talk to your local authorities, starting with the inspection office.

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