Need advice on venting a mop sink.

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by mliu, May 14, 2019.

  1. mliu

    mliu Member

    Joined:
    Feb 7, 2007
    Location:
    Colorado
    Ok, on to Round 2. I've abandoned the idea of using a combination waste and vent design (even though I'm under IPC, which seems much laxer than the UPC on this subject). To further simplify the DWV, I have Hand Sink #1 draining indirectly into Floor Sink #1, and Hand Sink #2 draining indirectly into the Mop Sink. That is why they are no longer pictured here.

    But I'm stymied by the mop sink, which is floor-mounted on the concrete slab. The only place I can see getting a dry vent to its drain pipe is from the wall behind it, but that would require a (short) horizontal vent section under the slab. The only other possibility I can think of is to connect Hand Sink #2 (not pictured, but just to the side of the mop sink) directly to a drain pipe, running the vent for the hand sink in the wall, and then connecting the Mop Sink drain to the hand sink drain, thus making the hand sink drain into a wet vent.

    Advice and recommendations, please!

    DWV Plan.png
     
  2. hj

    hj Moderator & Master Plumber Staff Member

    Joined:
    Aug 31, 2004
    Occupation:
    Plumber
    Location:
    Cave Creek, Arizona
    Simple. Run the mop sink drain UNDER the wall. Install the vent and then offset out to the trap location. It's the way plumbers have done it for decades.
     
  3. Sponsor

    Sponsor Paid Advertisement

     
  4. mliu

    mliu Member

    Joined:
    Feb 7, 2007
    Location:
    Colorado
    I'm not sure what you mean by "offset out to the trap." Wouldn't the trap be before the vent in the wall? Did you mean "offset out to Wye-6"?

    I'll have to see if there is enough available fall to do this.
     
  5. mliu

    mliu Member

    Joined:
    Feb 7, 2007
    Location:
    Colorado
    I've been reading some other posts in this forum where lavatories are used to wet vent other fixtures in bathroom groups (e.g., tubs & showers), so I'm wondering why can't I use my hand sinks to wet vent my mop sink and floor sink.

    DWV Plan 2.png

    Is this acceptable? The vents are at the inverted red triangles. The fixture drains from the hand sinks would be up-sized to 2". Wye-7 and Wye-8 would be rotated 45-deg so the wet vent pipe from the hand sinks would enter at an elevated position relative to the mop sink's & floor sink's fixture drains.
     
  6. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    You're allowed to wet vent residential bathroom groups on the same level. That doesn't apply to commercial fixtures.
    Also residential fixtures that that can't be wet vented are kitchen sinks, dishwashers, washers.

    What hj describes is how I would do it.
     
  7. mliu

    mliu Member

    Joined:
    Feb 7, 2007
    Location:
    Colorado
    Thanks for the additional info.

    I'm not exactly clear on what HJ is describing.
     
  8. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    Instead of running straight to the drain location, figure out where you "can" put a vent, head there and then make your way to the drain location.
    Cleanouts needed every 135 degree of change. That's one 90 and a 45.
     
  9. mliu

    mliu Member

    Joined:
    Feb 7, 2007
    Location:
    Colorado
    Like this?

    Mop Sink Drain.png

    I could put a cleanout in the wall coming off the pictured 2" dry vent line (red) before reducing the vent to 1-1/2".

    .
     
  10. hj

    hj Moderator & Master Plumber Staff Member

    Joined:
    Aug 31, 2004
    Occupation:
    Plumber
    Location:
    Cave Creek, Arizona
    After you install the "combo" on its back for the vent, put a 45 into the end of it, and the "P" trap into it.
     
    mliu likes this.
  11. hj

    hj Moderator & Master Plumber Staff Member

    Joined:
    Aug 31, 2004
    Occupation:
    Plumber
    Location:
    Cave Creek, Arizona
    You are making it difficult. Move the drain for the mop sink to the "left" so it is under the wall.
     
  12. mliu

    mliu Member

    Joined:
    Feb 7, 2007
    Location:
    Colorado
    And then a long-turn elbow out the other end of the sanitee so everything is on the same horizontal level? But then I think I'll have problems with a cleanout.
     
  13. mliu

    mliu Member

    Joined:
    Feb 7, 2007
    Location:
    Colorado
    I'm not sure what you mean by "move the drain for the mop sink to the 'left' so it is under the wall." The drain for the mop sink is in the center of the sink's basin.
     
  14. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    The cleanout can be on the vent and reduce afterwards.
    What you have on #7 works. HJ is just thinking that if you didn't use the 90 and vent above it vertically, you could use a combo pointing upward instead for the vent. Either way it's getting the cleanout.
     
  15. mliu

    mliu Member

    Joined:
    Feb 7, 2007
    Location:
    Colorado
    Does this check out?

    Mop Sink Drain 2.png

    I don't think the 2" Test Tee is actually needed for a cleanout since IPC 708.1.5, Exception 1 states that the P-trap can be removed and the 2" x 1-½" x 1-½" SaniTee can serve as the cleanout for this drain.

    .
     
  16. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    I think that would function well, but will not pass because you need a vent for the floor sink that is not carrying drainage.
     
  17. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    That's not a bathroom group. The inspector won't pass it.
     
  18. mliu

    mliu Member

    Joined:
    Feb 7, 2007
    Location:
    Colorado
    I'm at a loss to understand why this is not permissible per Section 911 of the IPC.

    IPC 911.3 Connection at different levels.
    Where the fixture drains connect at different levels, the vent shall connect as a vertical extension of the vertical drain. The vertical drain pipe connecting the two fixture drains shall be considered to be the vent for the lower fixture drain, and shall be sized in accordance with Table 911.3. The upper fixture shall not be a water closet.​
     
  19. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    It may be that IPC is different in that respect than UPC.
    I think it would work, as the hand wash station is going to have very little water being used. I'm in Washington State, so my codes here are a little different. I'm hoping an IPC plumber takes a look.
    There is I think it works, and then there is will it pass your local inspection. It might.
     
  20. mliu

    mliu Member

    Joined:
    Feb 7, 2007
    Location:
    Colorado
    Thank you for your reply and assistance. I understand that codes vary and do not always agree. I also understand that what appears to make sense may not necessarily be code compliant. I'm not trying to be argumentative or challenge the correctness of the code, I'm just trying to understand the code.
     
  21. mliu

    mliu Member

    Joined:
    Feb 7, 2007
    Location:
    Colorado
    Even though my jurisdiction has adopted the IPC, I was curious to read what the UPC stated about wet venting. Based on my reading of the 2018 UPC, vertical wet venting would be permissible outside of bathroom groups. (However, horizontal wet venting is discussed only in the context of bathroom groups.)

    UPC 908.0 Wet Venting
    908.1 Vertical Wet Venting.
    Wet venting is limited to vertical drainage piping receiving the discharge from the trap arm of one and two fixture unit fixtures that also serves as a vent not exceeding four fixtures. Wet-vented fixtures shall be within the same story; provided, further, that fixtures with a continuous vent discharging into a wet vent shall be within the same story as the wet-vented fixtures. No wet vent shall exceed 6 feet (1829 mm) in developed length.

    But then, my configuration would be disallowed under UPC 908.1 because, according to UPC Table 702.1, a Mop Sink is rated at 3 DFUs.
     
Similar Threads: Need advice
Forum Title Date
Plumbing Forum, Professional & DIY Advice Need advice for dealing with old in-slab toilet drain Sunday at 11:00 AM
Plumbing Forum, Professional & DIY Advice Need advice on DWV layout for small cafe (commercial space) May 8, 2019
Plumbing Forum, Professional & DIY Advice Remodel: need advice for adding /removing tees to existing copper drain Feb 6, 2019
Plumbing Forum, Professional & DIY Advice Need Advice: Pressure Balancing Loop vs... Jan 24, 2019
Plumbing Forum, Professional & DIY Advice Need advice on reconfiguring plumbing vents Jan 8, 2019

Share This Page