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Thread: Concern for basement p-trap connection to main line

  1. #1

    Question Concern for basement p-trap connection to main line

    Hello helpers and others like me(in need of help),

    The attached diagram will explain the general situation but the core question is this: I am concerned there is a possibility of toilet waste making its way into the basement floor p-trap, if the wye it's connected to is in perfect horizontal allignment with the main pipe.

    The main pipe will have a 1/4" per foot drop, but if a piece of solid hangs just past the wye, isn't there a chance some fluid may back up into the trap?

    Can the wye be rotated 1/8 from horizontal, then add a 1/8 bend before attaching the p-trap? (this would raise the p-trap slightly but I still have room under the concrete).

    Bottom line, what's the right way to do this?

    Regards, Greg
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  2. #2
    Plumbing Designer FloridaOrange's Avatar
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    The only way you'll have backup into your floor drain is if your main system backs up. Not sure about where you are but here (Florida) all 3 inch lines are only required to be sloped at 1/8" per foot. I would be more concerned about the distance from your water closet to the vent and by the fact you're washing the water closet unvented past your floor drain Edit - now I see your 2" vent.
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

  3. #3

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    Thanks for the input FloridaOrange. I'm up in Illinois, where in-ground mains are 4" and required to be 1/4" per foot. To clarify my drawing, the object on the east (terminating end) of the line is a septic lift tank (vented). The distance from the closet to the 2" vent is about 3.5'. Incidentally, this vent will also serve to drain a small bathroom sink. The whole run is about 9'.

    I doubt this info will change your view, which is very encouraging to me. So I think you're telling me it should be OK to place that wye in a "flat" horizontal postion? I just want to make sure I understand your advise correctly, because the thought of breaking up the concrete (again) is very unpleasant.

    Thanks again.

    greg_de

  4. #4
    Homeowner geniescience's Avatar
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    send a PM to one or two senior plumbers, asking if it is wise to rotate a little upwards the P trap arm Wye. Keep it short.

    I don't think you'll need the additional 1/8 bend.

    David

  5. #5
    Plumbing Contractor srdenny's Avatar
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    Putting a check valve in the floor drain might ease your concerns. BTW: Where's the vent for the floor drain trap?

  6. #6
    In the Trades Gary Swart's Avatar
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    You're right, if the main sewer backs up, it will come up the floor drains. Swing gate type check valves are not very satisfactory because over time with not use, these get fouled with lint and when the sewer backs up, it does so gently, and the check valve fails to stop the crud. I had that happen to me years ago, so when I reworked my basement plumbing, I installed floor drains that use a plastic ball that will float up and block the drain in case of a backup. They seem pretty foolproof. When the drain is in use, the ball rest in the bottom of it's compartment and the water flows around it. My city sewer department has watched the main sewer very closely for the years since my problem which was caused by a grease trap in a fast food restaurant failing, and I've had no problems since. I'd suggest you explore this type of floor drain.

  7. #7

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    Sounds like a backflow preventing valve is the most popular solution on this question. I actually looked at a swing gate type valve this morning and I have to agree it doesn't look foolproof. I will look around for the floating ball variety that was mentioned. Secondly, I will also look into rotating the wye up slightly since my downstream run is very short and terminates in a septic pump pit (in the basement).

    To answer SRDENNY's vent question: one 2" vent 6' downstream in the septic pit and one 2" vent/drain 1.5' upstream from wye where p-trap attaches. I assumed this would be adequate.

    Thanks all.

  8. #8
    Plumbing Contractor srdenny's Avatar
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    "To answer SRDENNY's vent question: one 2" vent 6' downstream in the septic pit and one 2" vent/drain 1.5' upstream from wye where p-trap attaches. I assumed this would be adequate."

    It all depends on which code your working with. The addition of the UPC which I am required to follow (2000) requires a separate vent for every trap and no horizontal wet venting. The septic pit (ie. ejector tank?) would be required to have it's own dedicated vent.

  9. #9

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    SRDENNY: Thanks for keeping me honest regarding the venting. I have been consulting the Illinois Plumbing Code (2004). I read the thing nearly completely, and did not see a strict requirement for a vent per trap. However, based on the total Fixture Unit value of the installed items (closet, sm. lav and floor drain), all within a 5' run, the code tables seem to indicate a 2" vent (it serves nothing else) is OK. I hope I read the tables correctly! Sound reasonable to you? And as you said, the ejector pit is 2" vented seperately.

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