Teeing water supply and drain for double vanity

[Unclejunebug]

I am replacing a single sink vanity with a double sink vanity. The current water lines and drain configuration line up with drawers in the middle of the new vanity which won't work. I am hoping to be able to tee off the water and drain to accommodate the two sinks.

What I currently have behind the wall is shown in the image below. The vent going up the wall and the drain going down are both 1-1/2" pipe...

Initially I thought I could use a double sanitary tee to do this but I have been seeing lots of info that states a double fixture tee is the correct way. All the double fixture tees I have found that have 1-1/2" fittings have a 2" fitting on the bottom but as mentioned above, my drain going down the wall is 1-1/2" pipe.

Can I use the double fixture tee with a 2" to 1-1/2" coupler on the bottom? Can I stack two sanitary tees on top of each other and run the two drains that way? What's the best way to accomplish what I need?

Thanks in advance for any help!

 

[Terry]

A double santee would be a very bad idea. There is no way to clear those trap arms when they gunk up.
A double lav using a double fixture fitting assumes you have 2" on the bottom, you have 1.5"
My fix on remodels has been the picture below. Does it pass code? Not really as the inspector still wants to see a 2" pipe there. It is the best you can do though with what you have unless you open floors and walls and find a 2" line.

This configuration is easy to snake later.
The two vents tie back together at six inches above the flood level of the sinks. Most of the time, that's at 42" above the floor.

 

[Sponsor]

 

[Unclejunebug]

A double santee would be a very bad idea. There is no way to clear those trap arms when they gunk up.
A double lav using a double fixture fitting assumes you have 2" on the bottom, you have 1.5"
My fix on remodels has been the picture below. Does it pass code? Not really as the inspector still wants to see a 2" pipe there. It is the best you can do though with what you have unless you open floors and walls and find a 2" line.
...
This configuration is easy to snake later.
The two vents tie back together at six inches above the flood level of the sinks. Most of the time, that's at 42" above the floor.

Wow, thank you very much for this info! I have no plans to open up the floor to look for a 2" pipe but I will at least remove the drywall all the way to floor. If I don't find a 2" pipe at the floor it looks like I'm taking off some more drywall.

Is the "six inches above the flood level of the sink" measured from the top of the countertop or where the top of the undermount sink and the bottom of the countertop meet? The counter height of my vanity is 34".

 

[Terry]

Flood lever is the highest level that the water can be in the sink, or countertop if it's an undermount.
34" plus six would be 40".

 

[Unclejunebug]

Flood lever is the highest level that the water can be in the sink, or countertop if it's an undermount.
34" plus six would be 40".

Perfect, thank you!

 

[Unclejunebug]

The drain pipe is 1-1/2" inches at the floor so it looks like I'm going the remodel route you showed above. A few more questions so I'm armed with enough info before I start cutting into anything...

1. How strict is the "six inches" above flood level? I imagine I don't want it to be less than that, is it OK to be over 6 inches above flood level?
2. Would you expect the vent to be attached to something above? I'm curious if the vent pipe will "drop" when I cut into it and if I need to suspend it while installing the new vent pipes.
3. The image shows the vent assembled outside of a wall which makes things easy to put together. If doing this with things already in place would you expect there to be enough "play" in the vent pipe where I could get all ABS couplings in there without much trouble? Or would you expect to need some kind of neoprene coupling like this in there somewhere? If the vent is not attached to anything above then I wouldn't expect there to be any issue with reassembly.

1. Everything I've read suggests a need for 1/4" of fall for every foot of drain. I assume this applies to ALL horizontal drain pieces so whatever I add inside the wall will need an adequate amount of fall built into it?
2. The T's in your image look like standard Sanitary Tees. Is this correct? Anything special about the Wye's?

Thanks again for all your help!

 

[Terry]

Shielded couplings work well when you can't spread the pipes apart.
Standard wyes and standard santees.
Horizontals get 1/4" per foot grade.

You can tie the revent higher but not lower.

If you have ABS in the wall now, it's likely not going anywhere. It's light stuff.

 

[Unclejunebug]

Shielded couplings work well when you can't spread the pipes apart.
Standard wyes and standard santees.
Horizontals get 1/4" per foot grade.

You can tie the revent higher but not lower.

If you have ABS in the wall now, it's likely not going anywhere. It's light stuff.

Most excellent, thank you very much, Terry! I'll pick up a shielded coupling as well as standard ABS couplings and use what works.