Re-route washing machine drain - vent question

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Kevin121, Jan 10, 2021.

  1. Kevin121

    Kevin121 Member

    Joined:
    Jan 5, 2021
    Location:
    Northeast PA
    Hello - I am looking to re-route my washing machine's drain line from the main septic drain to a separate drain/location. The question I have is regarding the vent for my toilet that is the next fixute "downstream" of the existing washing machine drain. The attached pictures probably illustrate the setup better than I can explain, however currently the washing machine has a P-trap and branch vent on an interior wall on the main floor. The drain goes through the floor into the basement and transitions to 3 inch diameter a the wye (with cleanout attached). This is where the main septic drain begins (most upsteam). The main drain runs about 2 feet or so and then picks up the toilet drain on the next wye. The main drain continues about another 4-5 feet (not visible in the picture) and then picks up the drain and another vent for the Tub/Shower unit and the bathroom sink located next to it. This vent goes up to the crawlspace and joins a horizontal section of pipe from a 2nd bathroom before going vertical and through the roof.

    My question is whether I relocate the washing machine drain so that it does NOT drain into the main septic drain will that cause an issue with the venting for the toilet that is the next fixture "downstream" in the drain line, or would the toilet be using the next vent downstream in the bathroom from the sink and tub/shower? All the diagrams I have looked at online seem to show the toilet's vent either at it's drain point, or beyond it (downstream) in the main drain. I have not seen diagrams showing a vent located before the toilet in the drain system, which in my case would be the washing machine drain. The existing branch vent would remain in place for the washing machine.

    Let me know any questions or clarifications needed.

    Links to pictures (Could not attach them here):

    https://drive.google.com/file/d/1TOSxLNPf-f03H8i2xIQzdJVfifJXCuFk/view?usp=sharing
    https://drive.google.com/file/d/1Oz-bRQnxSnBuskusGtS7qZLjxC0-lT_H/view?usp=sharing
    https://drive.google.com/file/d/1OnPKtXAN6i_ZPNu2zCNalTHNxKrCTKDI/view?usp=sharing

    1/11 Additonal pictures:
    https://photos.app.goo.gl/sevDKK7yYNucoUrF8
     
    Last edited: Jan 11, 2021
  2. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Not following what the 3" drain does downstream of the toilet. But your current arrangement is not compliant with the IPC. The toilet needs a vent before the washing machine drain comes in, and it can't be wet vented by the washing machine. So moving the washing machine drain elsewhere would be a good thing. Depending on what the 3" drain does downstream, the toilet may then end up wet vented by the next fixture.

    Cheers, Wayne
     
  3. Sponsor

    Sponsor Paid Advertisement

     
  4. Kevin121

    Kevin121 Member

    Joined:
    Jan 5, 2021
    Location:
    Northeast PA
    Thanks Wayne - I'll try to get some additional picture tomorrow of where the next vent is downstream.

    So am I correct in my assumption of a toilet not being able to have a vent prior to it? It must be either vented at the toilet drain ( tee into a vertical vent/drain) or the vent must be after (downstream) of the toilet?
     
  5. Jeff H Young

    Jeff H Young In the Trades

    Joined:
    Feb 27, 2020
    Location:
    92346
    (The wet vent wouldn't have been permitted ran in that fashion any way as it must remain horizontal and upon going vertical remain so until 6 inches above flood level of fixture) think this statement was false apologize for misinformation
     
    Last edited: Jan 12, 2021
  6. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    The toilet can be vented by having a dry vent come off, or by joining a vented drain (wet venting). A dry vent has to come off the drain vertically, it can't just be a horizontal upstream extension of a combo, say.

    Wet venting is restricted to bathroom fixtures, so you can't use the laundry drain for that. If the laundry drain had been a shower drain or a lavatory drain, then the toilet would have been properly wet vented via the arrangement visible in your picture (independent of what is downstream).

    Cheers, Wayne
     
  7. Kevin121

    Kevin121 Member

    Joined:
    Jan 5, 2021
    Location:
    Northeast PA
    Since this is a new build I assume the contractor is building to code and only using the vent on the washing machine for the washing machine. The toilet's vent must be the next vent downstream that serves the sink and tub/shower (wet vent).

    This gives me more confidence in re-routing the washing machine drain and not having any toilet vent issues as a result. I'll post a couple more pictures tomorrow of the other fixture drains.
     
  8. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    That would work fine if the laundry were connected downstream of the toilet, sink, and tub/shower. The current arrangement is not code compliant.

    Cheers, Wayne
     
  9. Kevin121

    Kevin121 Member

    Joined:
    Jan 5, 2021
    Location:
    Northeast PA
    Assuming I dont change the WM drain, what specifically is not code compliant in this case? If the toilet is getting it's (wet) vent from the downstream vent (my assumption) for tub/shower and sink, what makes it's out of code? Just trying to educate myself more. Home is being built by a very reputable local custom home builder and has passed all code inspections to date so I am very curious about this.

    If I change the WM drain to drain elsewhere and remove from main drain than is the toilet still vented properly to the downstream vent?
     
  10. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    A fixture drain needs to be vented before (dry venting) or as (wet venting) it joins another drain. Since the laundry drain is not allowed to wet vent the toilet drain, the laundry drain needs to join in after the toilet drain gets its vent. Which is presumably a wet vent at the connection of the next downstream fixture, to be confirmed with the additional photos.

    Cheers, Wayne
     
    Jeff H Young likes this.
  11. Kevin121

    Kevin121 Member

    Joined:
    Jan 5, 2021
    Location:
    Northeast PA
    I updated the post and included additional pictures. The first one should be in the bathroom with the sink and tub/shower drains and vents for each of those fixtures, the 2nd picture is zoomed out and shows the toilet drain on the left side and the drains for the sink and tub/shower on the right. The close up picture shows the tub/shower with it's own vent.

    For my own curiosity (and non-plumber brain) I'm curious why the laundry drain is not allowed to wet vent the toilet drain? I've seen examples on the forum where it looks like the toilet vent is upstream on the main drain instead of further down the main drain and the feedback appeared to acknowledge that this arrangement was fine. In what cases is this allowed and not allowed?

    You mentioned that if a shower drain was in place of where the laundry drain is then the wet vent would work so I'm confused why the laundry drain causes an issue while another fixture it its place wouldn't for a wet drain.

    I've also seen references that a toilet has to be the most upstream fixture in the drain system for wet venting, but I would like to understand why this is the case. I'm more visual so any pictures or diagrams to help explain all this are appreciated.
     
    Last edited: Jan 11, 2021
  12. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Your bathtub p-trap looks odd to me, seems to be made out of 3 quarter bends. Not sure if that's kosher, I suggest cropping the image so you can upload it here to appear without following an external link, and maybe starting a new thread with that question.

    So if you remove the washing machine from the WC drain, then the bathtub downstream is dry-vented and it will wet vent your WC. [There's a small amount of uncertainty in my understanding about that, in that the bathtub drain from the vent take-off (the san-tee) goes vertical - horizontal - vertical before hitting the WC drain. While a typical lavatory drain wet vent goes just vertical - horizontal. And there's a document from the city of Seattle calling out vertical-horizontal-vertical as prohibited, but the document doesn't provide a reference, and I don't see why it would matter or anything in the relevant language that prohibits it.]

    Good question, I don't know the answer, but the IPC and UPC both limit horizontal wet venting to using one bathroom fixture to wet vent another, and laundry drains are excluded. It may be related to the fact that a clothes washer pumps out water very quickly, while a shower or lavatory drain by gravity.

    On the WC location on a horizontal wet vent, the IPC and UPC differ. The UPC requires it to be the last (downstream-most) wet vented fixture, while the IPC doesn't impose that restriction.

    Cheers, Wayne
     
  13. Kevin121

    Kevin121 Member

    Joined:
    Jan 5, 2021
    Location:
    Northeast PA
    Thanks Wayne - So it sounds like I can assume that the shower/tub is currently the wet vent for the toilet , and by removing the laundry drain and draining elsewhere it will not negatively affect any venting for the toilet or anything else? Thanks for the help again.
     
    Jeff H Young likes this.
  14. Kevin121

    Kevin121 Member

    Joined:
    Jan 5, 2021
    Location:
    Northeast PA
    In either scenario (1.existing arrangement with laundry drain as-is, 2. re-routing laundry drain elsewhere) can the toilet be upstream of the Lav. and shower for horizontal wet venting? From the information I have seen the toilet should be downstream of those other fixtures. I did just find this in an IPC manual so I guess that eliminates some confusion I have - "Vertical wet vented systems are required to have the water closets as the most downstream fixture. This is not the case in horizontal wet venting."

    Would it be better to re-route the washing machine drain in the basement and use it's existing dry vent upstairs, or should I leave all the existing plumbing for the washing machine drain as-is (for additional venting?) and run a new standpipe, p-trap and vertical drain from upstairs into the basement? Obviously the latter option involves additional work but I would rather do that if it would provide any additional benefit over the other option.

    I think this comment from Jeff caused me confusion -
    Does anyone know what code this is in the IPC for the washing machine not being able to vent a fixture?
     
  15. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    https://wabo.memberclicks.net/assets/pdfs/Plumbing_Venting_Brochure_2018.pdf
    Horizontal venting for up to 2 bathroom groups is described starting page 12. A standpipe is not one of the items that can be involved in that.

    Common venting is described starting page 9, and is for two things. So if you wanted to vent something plus a standpipe, you may be OK, but that may require 3 inch below the standpipe. Or at least 3 inch below the lower fixture.

    Code describes what is permitted, but does not always enumerate what is not permitted.
     
  16. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    First, let me note that from a connectivity point of view only, the upstream most fixture is not well defined. Instead the upstream most two fixtures are defined, by the fixtures feeding the upstream most connection of fixture drains. In horizontal wet venting, one of those two upstream-most fixture drains must be the dry-vented fixture.

    As I said earlier, for the IPC, that is enough. The UPC, however, further requires that the WC be the downstream most fixture involved in a horizontal wet vent, so you may see references to that requirement. PA is on the IPC, to my knowledge. However, both would allow the order of WC + dry-vented bathtub (first two fixtures), then lav. Because the lav has a much higher p-trap and so must be individually vented, in this arrangement the only wet vented fixture is the WC.

    The former is fine and probably preferred.

    Do pursue the bathtub p-trap question.

    Cheers, Wayne
     
    Last edited: Jan 12, 2021
  17. James Henry

    James Henry In the Trades

    Joined:
    Jul 23, 2019
    Occupation:
    Plumber
    Location:
    Billings, Montana.

    The washer is an appliance that pumps water with great force. The drain that would be acting as a wet vent would be practically useless as a vent.
     
    Last edited: Jan 12, 2021
Similar Threads: Re-route washing
Forum Title Date
Plumbing Forum, Professional & DIY Advice Can this leak be repaired or need re-route? Nov 10, 2020
Plumbing Forum, Professional & DIY Advice Want to re-route washer/sink drain... question about vent. May 17, 2020
Plumbing Forum, Professional & DIY Advice Main line re-routed near electrical panel May 11, 2020
Plumbing Forum, Professional & DIY Advice Need to re-route sink drain but only fittings are exposed Jan 19, 2020
Plumbing Forum, Professional & DIY Advice Laundry Advice on Re-route Drain and Vent Feb 28, 2019

Share This Page