Need advice on venting a mop sink.

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Mliu

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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
 

hj

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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.
 

Mliu

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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.
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.
 

Mliu

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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.
 

Terry

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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.
 

Mliu

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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.
Thanks for the additional info.

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

Terry

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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.
 

Mliu

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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".

.
 

Mliu

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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.
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.
 

Mliu

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You are making it difficult. Move the drain for the mop sink to the "left" so it is under the wall.
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.
 

Terry

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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.
 

Mliu

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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.

.
 

Reach4

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I think that would function well, but will not pass because you need a vent for the floor sink that is not carrying drainage.
 

Mliu

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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.​
 

Terry

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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.
 

Mliu

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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.
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.
 

Mliu

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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.
 
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