Tying Lav 2" drain into back to back WC vent

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Loco Speedy

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Hi,

This is my first post and i apologize in advance for my lack of plumbing knowledge.

I am working on an older home with rotted out cast iron pipes that I recommended to be replaced with ABS. The single story home is on a concrete slab and has two back to back restrooms. The customer was insistant that the main trunkline/sewer line was good and only wants me to replace a portion of the cast iron piping - being all the bathroom fixture drains. So far, I replaced most of the vertical drains, just before they tie into the trunk line, but ran into some obstacles..Per customer request, demolision was not to be performed in one restroom. I was also given a time constraint, so it was decided not to replace the 3" cast iron double fixture fitting/flanges/drains for both toilets. I basically just cut the trap arm in the restroom i am allowed to break concrete in, and replaced a small section with 3" abs, 3x4" closet bend, and 4" toilet flange. Customer confusingly approved. Last fixture that i need to work on is the sink lavy in the restroom i that cant break concrete in.

This last fixture, the bathroom sink lav located where I cant jack hammer has a closet space directly the wall. Within the wall, its trap arm connects to a cast iron sanitary tee where it drains the waste water down below the concrete along with a 1.5" re-vent line above. Unfortunately for the customer's plumbing, the flooring inside of this closet was requested not to be jack hammered/dug. Drywall removal and rerouting the drain is the only option.

I was wondering if I could reroute the drain line from the sink lav into the dry vent section of the 3" vent that's shared by the two back to back toilets?? Will routing the lavy using 2" abs into the shared 3" vent for the back to back toilets work? All other fixtures have their own individual vent and it is 3.5 feet away.

Note: Im in California, so we use UPC plumbing code. Out of curiousity, will it work effectively even if its against code?

The height where the vent/lav drain connection would be 6" above the waterline level for the wc fixtures (correct me if im wrong but i think this is the toilet bowl height). The horizontal portion will be graded to give the drain a 1/4" drop for every linear foot.

My method of approach:
Raising the height of the 1.5" lav ptrap arm where it stubs in wall, connecting it to a 1.5x2" bushing, and then connecting it to a 2x2x1.5" 90 ell with 1.5" side inlet in order to bring the drain inside of the 2x4 wall. The 90 would be on the horizontal and the 1.5" inlet would face upwards. The upwards facing inlet will be attached to a 1.5" stick of abs where it would connect back to existing 1.5" vent using a shielded no hub band. I would then bore holes through a few 2x4" studs to direct the drain waste towards the 3" common vent such that the 2" lav drain will have the 1/4" slope. I will then use a 3x3x2" sanitary tee to tie the drain line into the vent the cast iron vent. I heard these vents can drop when cut so i'll be wrapping plumbers tape around the vent (tight) and fastenning the ends to the two adjacent studs, in hopes of achieving some support when cutting the vent with my grinder. The santee will be fitted in with 3" abs stub outs and 3" no hub bands.

Apologies for the long explanation. Ive been researching venting plumbing using the upc code as a guide and reading relatable forum posts on my downtime and I just can't seem to confidently wrap my head around it. I hope whoever is reading this can shed some insight, whether its in the form of chewing me out, telling me the obvious, etc, replies are greatly appreciated.

Thank you!
 
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Loco Speedy

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Thank you for the quick reply, here is a quick drawing. Hope it helps
 

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Loco Speedy

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Thank you for the quick reply, here is a quick drawing. Hope it helps

In the drawing, the middle line represents the main sewer line where i also used it as a line to split the plumbint layout for each bathroom.

Note: It looks like the back to back water closets have their own individual 3" vent. They do not. They share the same vent. As you can tell, i dont know how to draw these drain and vent diagrams
 

Reach4

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I was wondering if I could reroute the drain line from the sink lav into the dry vent section of the 3" vent that's shared by the two back to back toilets?? Will routing the lavy using 2" abs into the shared 3" vent for the back to back toilets work? All other fixtures have their own individual vent and it is 3.5 feet away.

Note: Im in California, so we use UPC plumbing code. Out of curiousity, will it work effectively even if its against code?
If I understand correctly, I think what you propose -- running the vented lavatory drainage into the common vent, would be allowed in IPC but not UPC. IPC lets you have two bathrooms as a group. I am not a pro.
 

Loco Speedy

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Thank you very much for referencing to the UPC code. I'm going to install and finish tthe job today.

Cheers
 

Reach4

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UPC does restrict horizontal wet venting to a single bathroom group, but what the OP proposes is vertical wet venting.
I would think vertical wet venting would be to have the trap arm from the lav go to a santee in the existing vent pipe.

I agree that what is proposed would work fine.
 

wwhitney

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I would think vertical wet venting would be to have the trap arm from the lav go to a santee in the existing vent pipe.
That would be typical, and if the horizontal lav fixture drain were short enough and fell only one pipe diameter, then the separate lav dry vent could be eliminated. But certainly adding the separate lav dry vent, or using one when the lav trap arm would be too long otherwise, is not prohibited and won't cause any problems.

The only wet vent in the OP drawing is the 3" stack between the double fixture fitting for the WCs and the san-tee/combo where the horizontal lav fixture drain joins in. So the wet vent is vertical.

Cheers, Wayne
 

Jeff H Young

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Both of the mentioned are wet venting a vent receiving waste from other fixtures and both comply one is just more common than other but not a problem at all
 
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