P-Trap missing in Washing Machine Drain

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Hansw, Mar 1, 2014.

  1. Hansw

    Hansw New Member

    Messages:
    2
    Location:
    Austin, TX
    Sewer smell in the laundry closet. I was expecting that the trap was missing, and after I opened up the wall, found out that indeed there is no P-Trap. There is also no visible venting. House is from the 1970s.

    photo.jpg photo (4).jpg
    As you can see from photo.jpg there is not a lot of space. So I've come up with a couple of solutions, but would like to hear comments and suggestions.

    1. Install P-trap. Keep the top part of the drain in the same location. Will need to go through the stud / remove stud on the left, to add some horizontal pipe to make it a P-trap. Then bend 180 degrees to come back, and let the waist go down into the sewer. (photo1.jpg shows part of that). Not sure how to install venting.
    photo (1).jpg

    2. Install 2nd washing machine outletbox, to the left of the existing one. I think I've 9 inches to the left of the stud. With the drain in the middle, the trap would not have any horizontal pipe (s-trap...). Maybe I can route the pipe to the end of the wall, so I would have 4 inches of horizontal pipe. Disadvantage: I need to go through the stud.
    photo (2).jpg

    3. Install drain completely to the left, in the corner, on the outside of the wall. In that case I have space for 4 inches of horizontal piping to make it a P-trap. Advantage: I would not need to go through the stud. Cheater valve could be installed under the existing box. Disadvantage: space is narrow, and washing machine could bang against the pipe and break the pipe.

    4. Install drain completely to the left, in the corner, inside the wall. In that case I have space for 4 inches of horizontal piping to make it a P-trap. Would have to go through the stud, and would have to build my own box inside the wall. Cheater valve could be installed under the existing box.

    I'm open to any comments and suggestions. Thanks for all your help!
    Last edited: Mar 1, 2014
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    A functioning p-trap must have the trap arm vented before it turns down, or you have a s-trap....all of your pictures effectively are s-traps, and those will siphon themselves and not likely solve your problem.
  3. dj2

    dj2 Member

    Messages:
    437
    Location:
    California
    Are you on a slab?
  4. asktom

    asktom Member

    Messages:
    589
    Location:
    Victor, MT
    Have you checked to be sure there is not a trap installed (incorrectly) under the floor? If there is it needs to be dealt with.
  5. jim mills

    jim mills New Member

    Messages:
    141
    Location:
    nebraska
    Typically takes two stud bays to fit the rough in. I just finished a job correcting that exact situation. Homeowner was pissed at the cost, and felt I did a bunch of unnecessary work. Smells gone though...

    Not my pic, but done just like this...
    rough in.jpg
  6. Hansw

    Hansw New Member

    Messages:
    2
    Location:
    Austin, TX
    Jadnashua: Yes I realize that I need it vented and need horizontal piping to make it working properly. Pictures are mostly to show scale and how much space I have.

    dj2: Yes I am on a slab

    asktom: I have not checked whether there is a trap installed under the floor. What is the best way to check for that?
    I did pour water down the drain. Without running the washing machine, the smell persisted over the next couple of days.

    Jim Mills: Your picture kinda shows what I envisioned in solution 3 and 4. Instead of vented to the top, having an air admittance valve.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    An AAV often doesn't work well with a pumped drain like a WM...the air needs somewhere to go, and it's getting pushed ahead of the stream. The AAV only lets air in, not out - to work well, it needs to be vented to the atmosphere (i.e., up to the roof, or where is may be able to tie in to the existing vent system - at least 42" above the floor or 6" above the flood rim of the highest thing being vented, whichever is higher).
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,242
    Location:
    Cave Creek, Arizona
    You figure out the venting FIRST, then work the drain around it.
  9. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,242
    Location:
    Cave Creek, Arizona
    quote; I just finished a job correcting that exact situation.

    Where do they find these original installing contractors? Phone numbers in a Crackerjack box? Or, a "we will save you hundreds of dollars on your installation" advertisement.
  10. jim mills

    jim mills New Member

    Messages:
    141
    Location:
    nebraska
    House bough by flippers!
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,242
    Location:
    Cave Creek, Arizona
    I guess that would be about the same thing, since they want to save "hundreds on the installation". All they are concerned about is HOW it looks after the paint is applied, now what goes inside the walls where nobody sees it.
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