Distance to air gap drain.

[Clutchcargo]

I have a 3 bay sink that I'm trying to work out the plumbing. This is for a garage based business. It's a detached garage and the drain connects to the plumbing in the house. One option for its placement is to put the sink against the adjacent wall to where the drain exits the building (see pic) and run the plumbing above the foundation, around the corner, and put the P-Trap (with air-gap) close to the "sub"-stack which is to the right of the mop sink. The problem is that the p-trap would be about 9' of pipe away from the closest drain on the 3 bay. Is this acceptable?
I guess I could add two AAVs one for the main drain next to the mop sink and the other just for the 3 bay but I'd rather just have one.
As always, any advice is hugely appreciated.

 

[wwhitney]

You need to specify your location or at least which plumbing code you are under.

But both the UPC and IPC would prohibit what you propose. IPC 1002.1 says that a fixture trap shall be within 24" vertically and 30" horizontal of the fixture outlet. While UPC 1001.2 says that in no case shall the tailpiece exceed 24". However, you could have the trap near the sink and run the trap arm around the corner to your drain connection.

What is your plan for venting the trap arm? The vent connection is required to be be within one trap diameter of fall from the trap outlet. I'm not understanding what purpose the AAV shown on a riser coming out of the floor could serve, it could only vent a fixture whose trap was below the floor.

Cheers, Wayne

 

[Sponsor]

 

[Clutchcargo]

Thanks Wayne, I'm in Vermont. UPC but no inspections other than health inspection.
I was hoping to put the trap right next to the riser (next to the mop sink) and run the drain from the 3 bay along the wall. It sounds like that's not doable because of the limitations from the fixture outlet. I had my doubts that it was allowed. What is the reason behind the limits of length from the fixture?

Assuming 1.5" PVC, does "one trap diameter of fall mean 6 feet? (1.5" divided by 1/4" per foot)

The AAV on the pipe from the floor is not permanent. I threw that on there to prevent sewer gasses from entering the garage while I work out the details. I suppose I could add a second AAV for the p-trap next to the 3 bay sink.

 

[wwhitney]

Thanks Wayne, I'm in Vermont. UPC but no inspections other than health inspection.

Up.codes says that Vermont uses the 2021 IPC, and the difference matters for some of your questions. Also, the UPC generally doesn't allow AAVs, although some states that have adopted the UPC have amended that.

What is the reason behind the limits of length from the fixture?

Not sure, but any gunk that would build up in the tailpiece would rot/smell with no trap to keep that out of the living space.

Assuming 1.5" PVC, does "one trap diameter of fall mean 6 feet? (1.5" divided by 1/4" per foot)

Yes for the IPC, although that requires you to get the exact slope of 1/4" per foot. Slope it more, you reduce the maximum horizontal. No for the UPC, as it further imposes a limit of 42" for a 1.5" trap arm.

If the laundry sink were to the right of your drain, you could run a horizontal trap arm from the triple sink, with an AAV within the distance limits discussed above, then around the corner, and join the trap arm of the laundry sink with a horizontal wye, using the triple sink to wet vent the laundry sink.

You could still do something similar with the laundry sink in the location shown--either run both trap arms to a double fixture fitting that is within 6' of both sinks, with an AAV on top, and come out of the bottom of the double fixture fitting to a LT90 to turn horizontal back towards the drain. Or stack a quarter bend (possibly street) above a san-tee above the slab entry--the quarter bend gets the AAV-vented triple sink from the right, the san-tee gets the laundry sink trap arm from the left. That would force your laundry sink trap to be fairly low, at most 1.5" above the san-tee inlet, which has to be below the triple sink trap arm.

Or you could just use two AAVs, would be simpler.

Cheers, Wayne

 

[Clutchcargo]

Up.codes says that Vermont uses the 2021 IPC, and the difference matters for some of your questions. Also, the UPC generally doesn't allow AAVs, although some states that have adopted the UPC have amended that.


Not sure, but any gunk that would build up in the tailpiece would rot/smell with no trap to keep that out of the living space.


Yes for the IPC, although that requires you to get the exact slope of 1/4" per foot. Slope it more, you reduce the maximum horizontal. No for the UPC, as it further imposes a limit of 42" for a 1.5" trap arm.

If the laundry sink were to the right of your drain, you could run a horizontal trap arm from the triple sink, with an AAV within the distance limits discussed above, then around the corner, and join the trap arm of the laundry sink with a horizontal wye, using the triple sink to wet vent the laundry sink.

You could still do something similar with the laundry sink in the location shown--either run both trap arms to a double fixture fitting that is within 6' of both sinks, with an AAV on top, and come out of the bottom of the double fixture fitting to a LT90 to turn horizontal back towards the drain. Or stack a quarter bend (possibly street) above a san-tee above the slab entry--the quarter bend gets the AAV-vented triple sink from the right, the san-tee gets the laundry sink trap arm from the left. That would force your laundry sink trap to be fairly low, at most 1.5" above the san-tee inlet, which has to be below the triple sink trap arm.

Or you could just use two AAVs, would be simpler.

Cheers, Wayne

The plumber I hired to install gas lines a few months ago said Vermont uses UPC code but you're right, I'm not sure he knew the difference.
Thanks for your expertise and ideas.