Single to double vanity

[Adam Smith]

Hi Everyone!

New to the forum. I spent my college years and a few years after in construction. Mainly remodels and have had the privilege of doing most aspects of construction. I bought a house last summer with an unfinished basement that the previous homeowner did partial work on. Most of what they did I've had to tweak to get it up to code and I'm seeing what looks like another area I will need to fix.

The existing homeowner wanted to change the builders rough in from a single to a double vanity which I will do as well. It looks like they were going to just extend the original drain pipe and add the second sink but that will pull the water out of the p trap closest to the main stack if I'm not mistaken.

I looked through the site and have no problem understanding how to convert the single to a double in most cases, but at the base of my stack I have the clean out which prohibits me from tieing in below where the original plumber connected the vanity waste, and I'm afraid if I tie in above, I will be too high once I drop the sink in. The sink waste pipe is 22" above the floor. How high is too high for a second pipe?

Can I pull from the vent stack to the left and tie into the far right sink? Or can two sinks not share one waste pipe even if the furthest sink from the stack has a vent? See attached pics with red indicating the proposed vent.

I also attached a pic I found on the site that is the closes scenario to mine expect they don't have a clean out where the two sinks meet the vertical pipe. As mentioned above, I can just tie in above the original plumbers, I'm just not sure how high I can go before I start running into issues with the sink.

 

[hj]

Your drawings do NOT have a vent for the left hand sink, so the flow is still going past an unvented connection.

 

[Sponsor]

 

[Adam Smith]

Sorry, if you look at image 6489, that horizontal pipe turns vertical right outside the picture. That's the main vent pipe.

 

[Adam Smith]

Here is a pic of the vent pipe.

 

[Adam Smith]

Thoughts anyone?

 

[Reach4]

Sorry, if you look at image 6489, that horizontal pipe turns vertical right outside the picture. That's the main vent pipe.

I think the problem is that the drainage coming into what would have been part of the trap arm for the left sink from the right sink messes up the plan. Maybe you could run a vent to the trap arm for the left sink before it joins the drainage from the right.

 

[Adam Smith]

I think the problem is that the drainage coming into what would have been part of the trap arm for the left sink from the right sink messes up the plan. Maybe you could run a vent to the trap arm for the left sink before it joins the drainage from the right.

I’m not following. I think it might just be easier to do the layout like the picture with pvc that I attached. My only concern is my right sink drain pipe will have to be above the left sink pipe and the left sink pipe is already at 20” to the top of the pipe. Once I put a T in my new drain pipe for the right sink will sit at 24” at the top of the pipe. Will this make it difficult putting in the p trap for the right sink?

 

[Reach4]

I’m not following.

I was thinking a long sweep combo horizontal in line with the black drain line. Then a wye with its leg pointing up to the vent, shown in green. Then the trap adapter.

I think it might just be easier to do the layout like the picture with pvc that I attached.

That works.

 

[Adam Smith]

I was thinking a long sweep combo horizontal in line with the black drain line. Then a wye with its leg pointing up to the vent, shown in green. Then the trap adapter.

View attachment 44190

That works.

So a vent where your green line is and then one where my red line is? Does your vent connect in between the two sinks?

 

[hj]

Your "vent" has nothing to do with the left hand sink. The water from the right hand one flows PAST it before it gets to the vent. Actually, it is NO BETTER than the original system.

 

[Adam Smith]

Your "vent" has nothing to do with the left hand sink. The water from the right hand one flows PAST it before it gets to the vent. Actually, it is NO BETTER than the original system.

Neither of your two responses have been helpful. Come back when you have something to contribute.

 

[Reach4]

So a vent where your green line is and then one where my red line is? Does your vent connect in between the two sinks?

Your red vent vents the right one.
Green vent vents the left.

Is that between? Semantics, so I am not sure which way to call it. It is not in the path of the drainage from the right sink. img_5.png tries to give the concept.

 

[Adam Smith]

Your red vent vents the right one.
Green vent vents the left.

Is that between? Semantics, so I am not sure which way to call it. It is not in the path of the drainage from the right sink. img_5.png tries to give the concept.

If I’m understanding the picture, does the vent connect to the left sink’s stub out?

 

[Reach4]

If I’m understanding the picture, does the vent connect to the left sink’s stub out?

Yes. It's not the only way. It is a way I think everybody would approve of functionally, and it seems like it might take less changing of what exists than some alternatives. It may not meet the aesthetics of some. I would be interested in seeing their more pleasing version.

I think there may be a problem with your tee anyway. I think you may need a medium or long sweep as you make the turn from horizontal to horizontal.

 

[Adam Smith]

I understand the concept of air behind water, but I guess I don’t understand how in this scenario my red line pipe wouldnt supply enough air. Won’t it prevent the right sinks water from siphoning the water out of the p trap on the left sink?