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Thread: Running a Washing Machine drain under slab

  1. #1

    Question Running a Washing Machine drain under slab

    Hello there,
    long time reader, first time poster.
    I'm about to do something that my gut is telling me to check with you guys and gals first. I'm moving my front loading washing machine inside my slab foundation house to a place that has no immediate drain. The closest drain is a bathtub about 8 ft. away. The main sewer line on the exterior of the house is about 16 ft. away. I was thinking about using the waterjet method to bore a hole in the dirt and meet up with one of the drains I've mentioned.

    I'd rather meet up with the main sewer line. Is 16 ft. too far for the water jet method? Is there another option that would be easier?

    Can you all give your two cents on this? Any precautions I need to know about?

    Thanks so much in advance!

    Daniel

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    So you are going to wash away the dirt under your slab floor?

  3. #3
    Plunger/TurdPuncher kingsotall's Avatar
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    I've never even heard of "the water jet method" so I guess I should just stay out of this one.
    You will need a vent and 2" standpipe with a trap.

  4. #4

    Default wash away dirt?

    yeah, I dont' know if this is leggit or not for interior plumbing. I've done this several times with outdoor landscaping pipe running under sidewalks/driveways. I don't plan on washing away too much dirt. Every other time I've done this in an outdoor setting, the amount of dirt displaced is not that substantial.

    kingsotall, btw, a water jet is where you plug one side of the pipe and drill a few holes in the plug and attach a hose to the other end of the pipe. The water pressure from the spigot shooting out the tiny holes cuts through the dirt and allows you to push the pipe rather easily underneath the ground.

    If you guys have never heard of this, what have you done instead?

    Thank you,
    Daniel

  5. #5
    In the Trades Gary Swart's Avatar
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    Cut the concrete out so you can trench and plumb the thing right. Even if you used your water jet to bore the hole, how are you going to get the pipe in the tunnel and then how are you going to keep it from sagging and making a low spot? You can hire a professional concrete company to cut the concrete or you can rent a saw that will do it. As already noted, you must use a 2" standpipe, a P trap, a vent, and tie into a sewer line that is at least 2".

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    DIY Senior Member TedL's Avatar
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    Consider whether draining into a "catch box" (I can't think of the right name) and pumping across the attic to the existing drain line might make more sense, price and disruption wise.

  7. #7
    Plunger/TurdPuncher kingsotall's Avatar
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    Unless it's in a basement I loathe the idea of using a pump to achieve drainage.

  8. #8
    Moderator & Master Plumber hj's Avatar
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    Default water jet

    Have you considered the fact, that if you are going to water jet a 12' distance, you need a 12' trench where you are jetting from for the jet pipe? If you intend to use short pieces glued together, there is no way you can be sure that they will make a straight pipe.

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    Plumbing Designer FloridaOrange's Avatar
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    Where are you located? Florida requires 3" pipe to the 2" trap on washers.
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

  10. #10
    In the Trades Gary Swart's Avatar
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    Are you saying to start with a 3" standpipe then reduce it to 2" at the trap? That is contrary to the principal of never reducing a drain size.

  11. #11
    DIY Senior Member chris8796's Avatar
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    I would cut the concrete, rather than trying to tunnel. Water jetting does not provide any control of pitch. Houses also have footings to work around. I've jetted plenty of sidewalks for irrigation, I couldn't imagine trying to go 16 ft with 2" schedule 40 under a slab house. I would be looking for a concrete cutter, preferably with a water-cooled hydraulic saw (no dust).

  12. #12
    Plumbing Designer FloridaOrange's Avatar
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    Quote Originally Posted by Gary Swart View Post
    Are you saying to start with a 3" standpipe then reduce it to 2" at the trap? That is contrary to the principal of never reducing a drain size.
    Not to hijack the thread but:
    It would be only reducing the drain size if you were to start with a 3" trap and then dump to a 2" standpipe.
    FPC 2007 406.3 Waste Connection. The waste from an automatic clothes washer shall discharge through an air break into a standpipe in acordance with Section 802.4 or into a laundry sink. The trap and fixture drain for an automatic clothes washer standpipe shall be a minimum of 2 inches in diameter. The automatic clothes washer fixture drain shall connect to a branch drain or drainage stack a minimum of 3 in diameter. Automatic clothes washers that discharge by gravity shall be permited to drain to a waste receptor or approved trench drain.
    The local AHJ interprets as a 3" up to trap, then a 2" trap (slab on grade).

    End hijack.
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

  13. #13
    In the Trades Gary Swart's Avatar
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    OK, I misunderstood what you were saying. The 2" standpipe and 2" trap have to connect to a 3" or larger drain. I read it as the opposite.

  14. #14

    Default sounds good

    concrete saw it is. Thanks for all of your input. I'll have to tear up the floor, but I wanna do it right.

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