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Thread: Drain line in slab has negative fall - what to do about it?

  1. #1
    DIY Junior Member silverado's Avatar
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    Default Drain line in slab has negative fall - what to do about it?

    Hi. I come seeking insight and advice. The 2 commodes in my 1970s home, which I just purchased last month, flush very slowly. Both rise slowly upon flushing, filling the bowl to the bottom of the rim lip (perhaps 1.25 inches short of overflow), then slowly go back down in a lazy spiral until finally completing with a loud, prolonged gurgle. Each commode does its job, flushing fully, every time and clearing all contents. Nevertheless, after living in the home for the first week and observing this, it didn't seem right to me and so I called a plumber.

    After determining that there was no blockage in the line, the plumber said it must have a "belly". They said they'd know for sure with a camera test. So they ran a camera and verified there is standing water in the line. Essentially, a one-way slope to the endpoint. They left me the video tape of the camera journey with narration.

    The drain line is about 75 ft from the outside clean-out to the most distant point, the master commode/tub drains. The last 30ft of the line slopes down in the wrong direction, and thus the last 10-15ft remains 100% full of water, 100% of the time. The hall bath line joins the main line at 61ft, still nearly 100% full at that junction. At about 58ft from the outside clean-out, the line is about 3/4 full and at 45ft it's mostly empty with what appears to be a small amount of water at the bottom of the line. From there to the clean-out and on past there to the city tap, the fall seems ok, holding only a small amount of water at the bottom, which the plumber says is normal.

    The home is a concrete slab foundation. My plumber doesn't do this sort repair and referred me to another plumber who came out and declined to take it on and referred me to another plumber who specializes in this sort of "tunnel" repair. Got the bid today for $29K to tunnel under the home, raise the line, and fill the tunnel with some sort of concrete slurry mix, as required by city code. I'm hoping there is a cheaper solution than that.

    I'm not a plumber so these may seem like dumb questions, but here goes.

    1) House is on a corner. City says there is a main line I could tap into on the downhill side of my house, near the rear corner. Since the line already slopes downward toward the back corner (master tub/commode are in back corner) of the home, could I not simply head the other direction with a new line from the master bath out to a new city tap? I realize this would require busting the slab open and accessing all the junction points to change the direction of the connecting pipes. That would include the points where the master bath, hall bath, and the kitchen line (which includes the washer drain) all meet the main line. Perhaps I'd have to seal the abandoned portion beyond where the kitchen line joins the main at 33ft from the clean-out? Is this a viable option to consider?

    2) Any other suggestions or ideas.

    Thanks a lot if you've read this far. I'm hoping there is a solution other than the $29K fix.
    Last edited by silverado; 08-25-2010 at 06:59 PM.

  2. #2
    Plumber jimbo's Avatar
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    Well, you have a big problem. Cutting in a new tap to the city.....first they will nick you pretty hard for permits, and that may involve digging in the street...never cheap!

    I would contact the famous law firm of Dewey, Cheatham, and Howe or another good real estate law firm. If you could prove the previous owner, and/or his real estate agent, had knowledge of this drain problem, you may have recourse. It would seem likely they would have been aware all these years that the toilets didn't work well! And did you have a home inspection? Did that raise any questions?

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    DIY Junior Member silverado's Avatar
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    Quote Originally Posted by jimbo View Post
    I would contact the famous law firm ....
    I don't plan on suing anyone, but even if I did, I still need to know my options and what it will cost.

    I wonder if leaving it as-is, since it has functioned this way for so many years without trouble (over 20 years according to the seller, with no backups or problems, and she never thought anything of it) would be the best thing to do. I just don't want to get stuck with a sudden problem and no game plan.

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    DIY Junior Member Stormrider49's Avatar
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    Well, I have to agree with Jimbo. In over thirty years as a broker I've seen lots of slow toilets, and there is always an underlying problem. If it is as obvious as you said in your original post

    "...rise slowly upon flushing, filling the bowl to the bottom of the rim lip (perhaps 1.25 inches short of overflow), then slowly go back down in a lazy spiral until finally completing with a loud, prolonged gurgle..."

    then your home inspector should have caught it. This is clearly an indication of a problem. If the inspector failed to catch it, then he and his E&O insurer have an obligation to you. Of course, if you didn't have an inspection then you assumed the liability.

    Someday, when you are ready to sell this house, you are going to have to disclose the problem, and either fix it or give the buyer a credit to have it fixed. You may as well take care of it now at the expense of the inspector, and enjoy trouble-free flushing during your ownership of the house.

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    DIY Junior Member silverado's Avatar
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    Thanks,

    Again, I know my legal options. What I'm looking for is plumbing advice.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    1. The line does NOT slope down in the wrong direction". It must slope upwards.
    2. The solution is NOT to raise the pipe, which could be extemely difficult, if not impossible, but rather to lower the downstream section so the pipe which is holding water can drain.
    3. ANY alternative solutions would require that we be there and do our own evaluation of the system, and its environs.

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    Yes, you could probably reroute the other fixtures to a new sewer tap, but you'd need to check the cost of that. Technically, that's not an issue. You could also (assuming there's enough slope), reroute those lines outside of the slab and then connect to the existing line. this would probably be less expensive than making a new tap as you would only be breaking in at one point rather than many.

    If you have a post tension slab, cutting it is non-trivial. Those are more common in earthquake country, but could exist anywhere. These have cables run through it that are under high tension...cutting one could injure someone when the tension is relieved.

    There is a limit of how many turns you can make before you need a cleanout, but that could be handled.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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