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Thread: floor drain and washer sharing trap?

  1. #1

    Default floor drain and washer sharing trap?

    Hi,

    Am building a new laundry room in California.
    I really want to protect against overflows, so in addition to auto shut off valves for the washer supplies I am including a floor drain.

    I've read about trap primers and their use, and I also sense that folks don't like them. Those that feed from potable water waste that water, and that's a real problem in Calif right now.

    Can't a washer and floor drain share the same trap so that using the washer will keep the trap full? Can such a drain be plumbed so that the washer pump out will not spill out the floor drain?

    Thanks,
    Steve

  2. #2
    Consultant cwhyu2's Avatar
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    You can do what is called an inderect where the discharge from the washer
    is discharged above the trap of the floor drain.

  3. #3
    Forum Admin, Expert Plumber Terry's Avatar
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    The p-trap for the washer must be above the floor level, and it must have a standpipe.

    You can add a fitting on the standpipe the lets a bit of water flow down to the floor drain p-trap to act as a trap primer.

  4. #4

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    Quote Originally Posted by cwhyu2 View Post
    You can do what is called an inderect where the discharge from the washer
    is discharged above the trap of the floor drain.
    Thanks for the reply. I remember seeing that setup in restaurant kitchens in my earlier days.

    I'll do it that way if that is what is needed. If you don't mind a followup question...Is the indirect setup any different than piping the washer outlet into the line just upstream of where the floor drain enters its trap? I had asked about it overpowering the trap, but if that is going to overpower in this setup, then would it also overpower in the indirect setup?

    Thanks again.

    Steve

  5. #5

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    Quote Originally Posted by Terry View Post
    The p-trap for the washer must be above the floor level, and it must have a standpipe.
    Okay. It doesn't need to be accessible, though, right?
    Quote Originally Posted by Terry View Post
    You can add a fitting on the standpipe the lets a bit of water flow down to the floor drain p-trap to act as a trap primer.
    Okay. Thanks! That'd be good, but my naive guess is that I'd have a problem with lint filling that fitting and eliminating the priming. Sorry -- I've never had a trap primer in my hands to look at.

    Steve

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    Forum Admin, Expert Plumber Terry's Avatar
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    Thanks for the reply. I remember seeing that setup in restaurant kitchens in my earlier days.
    Commercial kitchens will have floor sink that takes the drainage from a food prep sink.
    But that isn't a washer. A washer had a problem with suds.
    Dumping a washer into a floor drain, you would have suds all over the floor.

  7. #7
    Consultant cwhyu2's Avatar
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    I was working on a drawing,but my program is not working properly.
    Like Terry said you do need a stand pipe,min 2" and if you floor drain is 3" you
    should not have a problem.

  8. #8

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    Quote Originally Posted by cwhyu2 View Post
    I was working on a drawing,but my program is not working properly.
    Like Terry said you do need a stand pipe,min 2" and if you floor drain is 3" you should not have a problem.
    My floor drain is just 2".

    I have some rework to do. (Yeah, I know. If I'd hired someone it'd be done correctly by now!)

    So, it seems the only option is the following?
    Washer 2" standpipe into non accessible P trap.
    P trap into 2" vertical vent line.
    Below the floor, the vertical vent line into drain line just downstream of the floor drain trap.
    There is no other venting in the immediate area.

    Trap will remain full due to trap primer sourced by a fitting in the standpipe above (?) the P trap.

    All good? Ugh. I think the floor drain's trap is going to get siphoned dry by the washer draining.

    Steve
    Last edited by steverino; 04-10-2009 at 01:45 PM.

  9. #9
    Master Plumber Redwood's Avatar
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    If the floor drain is not vented it could very easily get its trap siphoned by the washer...

    If the washer and the floor drain share the same 2" line with out increasing to 3 before where the floor drain ties in I see big problems....

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Default trap primer

    A pressure operated trap primer, as opposed to a flow operated one, only dribbles a very small amount of water into the trap every time the pressure fluctuates due to fixture use, so it does not really "waste" water. Or more to the point, you probably waste more water than that when you use your toothbrush.

  11. #11

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    Quote Originally Posted by Redwood View Post
    If the floor drain is not vented it could very easily get its trap siphoned by the washer...

    If the washer and the floor drain share the same 2" line with out increasing to 3 before where the floor drain ties in I see big problems....
    I'm not sure where the big problems would arise. If the washer needs a 2" drain, then a 2" drain should be sufficient for that entire line. There's nothing else draining into that line except the floor drain, and the only source of water for that floor drain is the washer.

    Steve

  12. #12

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    Quote Originally Posted by hj View Post
    A pressure operated trap primer, as opposed to a flow operated one, only dribbles a very small amount of water into the trap every time the pressure fluctuates due to fixture use, so it does not really "waste" water. Or more to the point, you probably waste more water than that when you use your toothbrush.
    Nice. I'll research more.

    Thanks!

  13. #13
    Master Plumber Redwood's Avatar
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    The problem would be that any slight restriction in the line could cause an eruption from the floor drain.
    Last edited by Redwood; 04-13-2009 at 09:35 AM.

  14. #14
    Forum Admin, Expert Plumber Terry's Avatar
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    I'm not sure where the big problems would arise. If the washer needs a 2" drain, then a 2" drain should be sufficient for that entire line. There's nothing else draining into that line except the floor drain, and the only source of water for that floor drain is the washer.
    I did some service work in the crawlspace of one house, that everytime the washer ran, soap suds would come out from under the toilet.

    I went underneath, and fixed some bad slope on some 3" waste.
    That seemed to fix it.

    Imagine a floor drain.

  15. #15

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    Quote Originally Posted by Terry View Post
    The p-trap for the washer must be above the floor level, and it must have a standpipe.

    You can add a fitting on the standpipe the lets a bit of water flow down to the floor drain p-trap to act as a trap primer.
    Thanks, all, for the great input you've offered. I'm working a bit too much in the dark on this one, so I'm arranging a consulting session with a local plumber. I'll count on him to provide a design to follow. He'll also check my other work. :-)

    One last question, though...

    Terry mentioned priming the floor drain trap with a takeoff from the standpipe. I really like that idea, but have one concern that you guys might help with. How much of a concern is it that the primer source fixture will cause a lint blockage in the standpipe?

    Steve

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