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Thread: How can I add a p-trap to finally resolve stinky laundry room!

  1. #1
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    Default How can I add a p-trap to finally resolve stinky laundry room!

    How can I add a p-trap to finally resolve an occasional but bad stink in the laundry room?

    It has been stinking badly on certain occasions, all the way into the kitchen sometimes, yech.

    I investigated fully yesterday and found the problem: there is no p-trap at all for the washing machine. When air pressure is low in the laundry room, sewer gasses are extracted from the drain and come in the house. Shower fan + dryer exhaust fan + closed door = low pressure in that room, causing air suction at the washer drain.

    I removed the wall in the basement and saw that the 3" piping just goes across and down into the concrete floor. No p-trap!

    I suppose all I need to do is saw at two places and insert a 3" diameter p-trap (which I hope exists?). However since this is a washing machine, it can drain a lot of water real fast, so I have concerns about:
    - how close/far away from the washer can I put the p-trap (4 feet down + 4 feet across = 8 feet, is that ok?)
    - do I have to check/add venting for a p-trap?
    - do I have to think about drain water backing up due to my p-trap?

    Whoever did the original plumbing also added a drain pipe (going to the garage for a sink but that sink never got installed) right next to the washer drain pipe. So that garage sink drain pipe is open and connected to nothing. Should I block it or will that cause new problems? Currently it stinks up the garage but the p-trap should prevent this in the future.

    Thanks so much for your knowledgeable advice!

  2. #2
    Master Plumber-Gas Fitter shacko's Avatar
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    Default Wash Machine Hook-Up

    >>>I removed the wall in the basement and saw that the 3" piping just goes across and down into the concrete floor. No p-trap!<<<<

    Just goes across what?, is this your main sewer pipe?

    >>>>I suppose all I need to do is saw at two places and insert a 3" diameter p-trap<<<<

    Why do you think you need a 3in. trap?

    >>>>- how close/far away from the washer can I put the p-trap (4 feet down + 4 feet across = 8 feet, is that ok?)<<<<

    Have you been draining your wash machine down into the line?

    I really can't get a grasp on what you have, can you post a picture?

    The only thing I can state for sure is that you have to cap the line thats in the garage, it's tied into a live sewer line, major health hazard.

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    In the Trades Gary Swart's Avatar
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    Default

    I don't have a clear picture of your situation either, but I can answer a couple of questions. A washer drain only needs to be 2". It is a very simple fitting that will reduce the 3" to 2". The trap must be directly under the standpipe, and yes, it has to be vented through the roof.

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    Default An illustration

    Thanks for looking into this, here are my responses:

    >>>I removed the wall in the basement and saw that the 3" piping just goes across and down into the concrete floor. No p-trap!<<<<

    >>Just goes across what?

    6 feet across, with a small angle parallel to the ground (illustration below shows this)

    >> is this your main sewer pipe?

    No

    >>>>I suppose all I need to do is saw at two places and insert a 3" diameter p-trap<<<<

    >> Why do you think you need a 3in. trap?

    I think it's easiest to stay with the existing size rather than get adapters for different sizes. But I want to do it the right way, which size is better?

    >>>>- how close/far away from the washer can I put the p-trap (4 feet down + 4 feet across = 8 feet, is that ok?)<<<<

    >> Have you been draining your wash machine down into the line?

    Yes, it's a standard washing machine drain, meaning a flexible u-pipe from the washer is loosely fitted into a larger pipe in the wall, that goes down the sewer line eventually.

    >> I really can't get a grasp on what you have, can you post a picture?


    Well here's an illustration of the "down 4 ft then across 6 ft then down 4 ft" drain pipe in the wall: no p-trap


    http://img97.imageshack.us/img97/2046/pipes.jpg

    >> The only thing I can state for sure is that you have to cap the line thats in the garage, it's tied into a live sewer line, major health hazard.

    Good, I'll do that.

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    Quote Originally Posted by Gary Swart View Post
    I don't have a clear picture of your situation either, but I can answer a couple of questions. A washer drain only needs to be 2". It is a very simple fitting that will reduce the 3" to 2". The trap must be directly under the standpipe, and yes, it has to be vented through the roof.

    I hope that's not an absolute requirement because that area is much harder to reach (e.g. water pipes in the way). That's why I would like to put the p-trap further away, along the (near) horizontal section, where I have easy access.

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    Plumber jimbo's Avatar
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    Default

    [quote=JeanGoulet;224699]I hope that's not an absolute requirement because that area is much harder to reach (e.g. water pipes in the way). That's why I would like to put the p-trap further away, along the (near) horizontal section, where I have easy access.[/quote]


    That you cannot do. It would be called a running trap, not allowed and drains very slowly.

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    Forum Admin, Expert Plumber Terry's Avatar
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    If you don't vent the p-trap with a pipe through the roof, or at least with an AAV, you will be right back to the start.
    A laundry room that smells.

    A trap will siphon dry without a vent.

    You do not get to pick up your yearly salary without installing a vent.

    2" drain and trap, 1.5" vent
    P-trap on the same floor as the washer.
    Attached Images Attached Images  

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    Jack of all trades frenchie's Avatar
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    Default

    Quote Originally Posted by JeanGoulet View Post
    I hope that's not an absolute requirement because that area is much harder to reach (e.g. water pipes in the way). That's why I would like to put the p-trap further away, along the (near) horizontal section, where I have easy access.
    I think you misunderstand. They mean upstairs, in the laudry room, behind the washing machine, on the actual standpipe.
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    Moderator & Master Plumber hj's Avatar
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    Default drain

    If your drawing is accurate and the washer drains into the top of that pipe, then there is no vent and any "P" trap will siphon and give you the same problem you have now. If it does not drain into that pipe, WHERE is the existing connection for the hose?

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    Default The vent is available, will the P-trap work?

    Quote Originally Posted by hj View Post
    If your drawing is accurate and the washer drains into the top of that pipe, then there is no vent and any "P" trap will siphon and give you the same problem you have now. If it does not drain into that pipe, WHERE is the existing connection for the hose?
    Yes, there is a vent, I didn't show it in the simplified drawing earlier, so I have included a more detailed one:



    Is that going to work?

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    Forum Admin, Expert Plumber Terry's Avatar
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    The vent must come off on the same level as the p-trap.

    A vent lower isn't going to stop the pipe from siphoning.
    It will still be like siphon gas from a car.

  12. #12
    Moderator & Master Plumber hj's Avatar
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    Default drain

    You are trying to get us to give a blessing for something which will not work. You do NOT put things where they are "convenient", you put them where they are supposed to be. Sort of like the drunk who was searching the ground for something. When asked what he was doing, he said, "I dropped my wallet and am looking for it." The other person started to help him look, and after about 15 minutes asked the drunk, "Are you sure you dropped it here?" And the drunk replied, "NO, I dropped over there by my car." When asked why he was looking where they were, he replied, "It's too dark over there. This place has better lighting." And the "vent" you show is completely ineffective for any purpose, other than to stand there and look pretty.

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    DIY Junior Member opensky's Avatar
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    Question Washing Machine Discharge piping height and venting questions

    Hi All,
    Sorry to bring this thread back from the dead but I have a very similar question. I'm renting an old farmhouse with a washer and dryer in the basement. The washer discharges into a barrel that is then pumped out with a sump pump. It smells awful and the pump doesn't always work properly and then it overflows. So, I was wondering how it would work to run a pipe over to the main line. The line that runs from the kitchen sink, connects at a pvc joint right before it goes into the basement wall which is about 6' above the ground. This joint is about 9' from where the washer currently sits. FYI, I have a newer (two years old) front load whirlpool washing machine.

    Question #1: Will the washer be able to pump the water up 6-7' and out?
    Question #2: Do I need to add a P-Trap or can I just add a vent? The P-Trap would increase the height further, so I was wondering if I could just vent it and skip the P-Trap.

    THANKS!

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    DIY Senior Member BobL43's Avatar
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    Quote Originally Posted by opensky View Post
    Please don't waste my time with such worthless responses.
    I think any water that sits in a barrel is going to stink after a while even if "new" wash water is added to it. Are you sure the front loader washer is not the source of the odor? These machines require additional maintenance to the front door seal, like wiping them dry and keeping the door ajar after a use. And some have a hair trap filter that needs to be drained and cleaned.
    I am definitely not a pro plumber, but I am a pro crastinator

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    In the Trades Tom Sawyer's Avatar
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    If the sink line is only 1 1/2" then the answer is no, the line is not big enough to handle the sink and the washer. If it is larger, say 2" or 3" then yes but you will also have to add a trap (2") and a vent 1-1/2"
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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