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Thread: Laundry drain pipe help for s-trap location. Canada

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    DIY Junior Member klrman's Avatar
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    Default Laundry drain pipe help for s-trap location. Canada

    Hi, I'm new here My house is very old and still has a 1 1/12 inch laundry drain pipe. It runs 40 feet across my crawlspace. I'm going to vent it and know how to do that correctly, but since the drain pipe is only 1 1/2 inches instead of the standard 2 inch and I need to re-locate it to the back wall, would it be more ideal to locate the s-trap lower than 24 inches from the top to offset possible back spill? I was thinking 36 inches or so but I'm not really sure.

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    Plumber krow's Avatar
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    Quote Originally Posted by klrman View Post
    Hi, I'm new here My house is very old and still has a 1 1/12 inch laundry drain pipe. It runs 40 feet across my crawlspace. I'm going to vent it and know how to do that correctly, but since the drain pipe is only 1 1/2 inches instead of the standard 2 inch and I need to re-locate it to the back wall, would it be more ideal to locate the s-trap lower than 24 inches from the top to offset possible back spill? I was thinking 36 inches or so but I'm not really sure.
    I 'm not really clear what you are asking.

    But, s-trap are not allowed anywhere in north America....... except maybe Mexico (maybe you mean p-trap) Let us know if you have a laundry sink in your set up. Regardless of whether you do or not, whether its 1 1/2" or 2 ", you need to install a clean out at the 20' mark beyond your p-trap or have access to 20' of pipe in both directions from a clean out (for rodding purposes.)

    To answer your original question , as best as I can understand it, (without a laundry sink) it can go at any hieght, prefferably a 2" diameter drain line. 36" - 40" is a comfortable height.

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    DIY Junior Member klrman's Avatar
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    Sorry I meant p-trap. No laundry sink. I just wasn't sure how low the p-trap should be from the top of the standpipe? (drainpipe for wash machine) if the standpipe is around 40 inches?

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    Forum Admin, Expert Plumber Terry's Avatar
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    Just increase the standpipe to 2"
    That will give you some added volume.

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    DIY Junior Member klrman's Avatar
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    Quote Originally Posted by Terry View Post
    Just increase the standpipe to 2"
    That will give you some added volume.
    Like 2" stand pipe, 2" p-trap running into the 1 1/2 inch drain pipe under the house?

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    Moderator & Master Plumber hj's Avatar
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    If the 1 1/2" line is inadequate, and I would suspect that a 40' horizontal line WOULD be, it will overflow regardless of the riser OR trap size.

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    Forum Admin, Expert Plumber Terry's Avatar
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    I've used a 2" standpipe over a 1.5" p-trap.
    Not inspected, but if the 1.5" standpipe is overflowing, and you can increase the size, then adding a larger receptor over the p-trap works sometimes.
    If the 1.5" drain is plugged, then nothing is going to work.
    I grew up in a home that had a 1.5" washer drain with a 12" riser.
    It flooded all the time.
    I bought the house next door, it also had a 1.5" washer drain, but I plumbed it with more height and it worked fine.
    In fact, most homes before 1960 had 1.5" washer drains.
    We don't do that anymore, the cost difference between 1.5 and 2.0 is nothing in the big scheme of things.
    Some like the IPC are now requiring 3" for suds control on the horizontal.
    I've also had pipe as large as 3" over a 2" p-trap that enabled me to put more drains into it.
    I've also installed floor sinks that I can put drains into.
    I've also installed laundry tubs that I can drain a washer into. The laundry tub has a 1.5" p-trap, and does just fine.
    It's all about adding more sizing for the initial push from the washer.
    Or in some cases, just a larger space to add drains to, like for soda dispensers or condensate drains.
    Last edited by Terry; 06-02-2010 at 01:43 PM.

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    In the Trades Gary Swart's Avatar
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    What am I not seeing here? This 1-1/2" drain runs 40 feet across a crawl space and you are relocating it. What prevents you from putting in a larger drain line? For a margin of safety, I'd consider a 3" line. You still have to have an appropriate clean-out, trap and vent, but those are necessities regardless of the size of pipe.

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    DIY Junior Member klrman's Avatar
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    Thanks for all the help and thanks Terry for motivating me to at least hope what I am doing may work!!! I am relocating the standpipe to the back wall of my laundry room instead the side wall where it is now. I was hoping by using a 2 inch standpipe, 2 inch p-trap and 2 inch drain pipe for about 12 feet under the crawlspace running into the 1.5 inch drain pipe that this may have enough volume to stop the overflow that is occasionally happening. My original standpipe had no venting at all, so hopefully with the new vent I installed as well it's all going to work.

    The reason I am not running 2 inch pipe all the way under the craw space is that, first, it's really hard to get to, second, it's quite a chore for me to change the connections where the drain pipe meets the main 4 inch drain pipe as the whole house is connected to the main 4 inch drain and thirdly, getting a plumber to do anything around my little town under $1,000 for crawl space work would be a miracle, and I just don't want to do that right now. If it still doesn't work, I can wait until it gets a little warmer up here in Canada, and then continue the 2 inch drain right through to the main 4 inch drain, regardless of all the spiders, bugs, rogue cats that live in my crawlspace and all
    Last edited by klrman; 06-02-2010 at 11:06 PM.

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    Plumber krow's Avatar
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    Its not really a good idea, as well as against code, to reduce the 2" to 1 1/2" down stream of the P-trap, especially on the horizontal run. It will be your primary spot for any future blockages.

    It will be only a temporary fix. Its only a question of time.

    Good luck, I hope it works out in your favour

  11. #11
    DIY Junior Member klrman's Avatar
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    Quote Originally Posted by krow View Post
    Its not really a good idea, as well as against code, to reduce the 2" to 1 1/2" down stream of the P-trap, especially on the horizontal run. It will be your primary spot for any future blockages.

    It will be only a temporary fix. Its only a question of time.

    Good luck, I hope it works out in your favour
    Yeah, I've been thinking the same thing, but if it buys me 2 months of hassle free washing, then I'll just run it all the way through later on when it gets warmer down there. Thanks for the advice.

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    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    There is a really simple solution to this problem that does not require you do do anything to your drainage....

    Put a restrictor on the discharge line of the washing machine so that it takes the washer longer to pump down. This will give you less water all at once.

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