Horizontal Double Wye Tee Fitting

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Jian

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I am trying to add a shower drain to an existing tub drain. The existing tub drain is 1-1/2'' and has a dry vent. I am wondering if I can use a horizontal double wye tee with a slope to merge the new shower drain to the dry vent and tub drain. I know horizontal double sanitary tee is not allowed in this case since there will be issues on backflow. What about horizontal double wye tee? I have attached the a drawing below to illustrate my idea. The top graph A is the existing plumbing and bottom B is my proposed plan.

Plumbing plan:
IMG_20201119_092824863.jpg


Double wye tee:
double wye tee.jpg

Double sanitary tee:
double sanitary tee.jpg

Another proposal I find is to use a Sanitary Tee with a side inlet. Can I position the side inlet upwards for dry vent and merge the shower and tub drain. See the drawing below for this proposal and pic for the sanitary tee with side inlet.
IMG_20201119_111936948.jpg


Sanitary Tee with Side Inlet
left-side-inlet.jpg

Considering suggestions below from Wayne and Reach4, here is the third proposal of the full bathroom if the 1-1/2'' drain pipe size is enlarged to 2''.
IMG_20201119_203512448.jpg
 
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wwhitney

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A couple things. Your first picture is a double wye, and your second picture is a double wye-45 tee or double combo (if it were all one piece of plastic). Anywhere you can use the first picture, you can use the second picture. A double sanitary tee has less sweep to the side inlets.

Your proposed drawing is a no go. It has a horizontal dry vent take off, that's not allowed. The only time a vent can connect horizontally is a wet vent; the fixture draining into the wet vent will prevent accumulation of solids.

But you can simply wet vent your tub (MA has it's own plumbing code, my cursory reading of 248 cmr 10.16(8) says it matches the IPC/UPC in this regard). You just join the shower into the tub drain with a flat wye after the tub drain vent take off. Preferably before the lav drain comes in, but a double wye with the lav would probably be OK. After the lav might be OK, too, but that would require a closer reading of 248 cmr 10.16(8) to be sure.

Cheers, Wayne
 

Reach4

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The thing you pictured is not a double sanitary tee.

Your vanity needs to be vented, and that can wet vent the bath and shower lines with no additional vent needed.

Is what you proposed with the wye is preferable to the other fitting, and I am not completely sure if it is OK or not. I think probably yes, but it is more complex than you need.
 

wwhitney

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Your vanity needs to be vented, and that can wet vent the bath and shower lines with no additional vent needed.
Massachusetts requires a wet vent to 2", like the UPC. So that's true if the existing lavatory drain and vent are 2". And I should amend my remarks to say that the wet venting I proposed is only an option if the tub drain and vent are 2".

Cheers, Wayne
 

Jian

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A couple things. Your first picture is a double wye, and your second picture is a double wye-45 tee or double combo (if it were all one piece of plastic). Anywhere you can use the first picture, you can use the second picture. A double sanitary tee has less sweep to the side inlets.

Your proposed drawing is a no go. It has a horizontal dry vent take off, that's not allowed. The only time a vent can connect horizontally is a wet vent; the fixture draining into the wet vent will prevent accumulation of solids.

But you can simply wet vent your tub (MA has it's own plumbing code, my cursory reading of 248 cmr 10.16(8) says it matches the IPC/UPC in this regard). You just join the shower into the tub drain with a flat wye after the tub drain vent take off. Preferably before the lav drain comes in, but a double wye with the lav would probably be OK. After the lav might be OK, too, but that would require a closer reading of 248 cmr 10.16(8) to be sure.

Cheers, Wayne

I agree with you a flat wye might be the best and easiest solution. But that will require adding another vent for the new shower drain? The main reason I am trying to use the horizontal double wye is so that the shower and tub drain can share the same vent. I have some space limits and don't want to expand the project scope in this case.
 

Reach4

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If vanity drain+vent can be two inch, all red lines are horizontal (~2% slope) 2 inch. Santee or wye at main stack.

2% is 1/4 inch per foot -- close enough.
IMG_5.jpg
 

Jian

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If vanity drain+vent can be two inch, all red lines are horizontal (~2% slope) 2 inch. Santee or wye at main stack.

2% is 1/4 inch per foot -- close enough.
View attachment 68000

But in this layout the shower drain does not have any vent. Will that be a problem when the vanity drains which will create negative pressure on the shower drain?

I also added another proposal in my main post using sanitary tee with a side inlet. Is it a possible solution?
 
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Jian

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Massachusetts requires a wet vent to 2", like the UPC. So that's true if the existing lavatory drain and vent are 2". And I should amend my remarks to say that the wet venting I proposed is only an option if the tub drain and vent are 2".

Cheers, Wayne

The existing lav drain and vent is 1-1/2''. I also added another proposal on the main post using sanitary tee with side inlet. I am thinking if the side inlet is positioned upwards and used for dry vent, that will solve the problem of possible horizontal dry vent.
 

wwhitney

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But in this layout the shower drain does not have any vent. Will that be a problem when the vanity drains which will create negative pressure on the shower drain?
The simplest venting method is to give each fixture drain its own dry vent takeoff. That leads to a lot of vents.

In wet venting, it is recognized that a pipe can serve as both the drain for one fixture and the vent for another fixture. So if you brought the new shower drain in to join the bathtub drain with a wye after the bathtub drain is vented, then the shower vent path is horizontal upstream in the bathtub drain, from the new wye to the bathtub dry vent take off, and then it uses the bathtub dry vent.

Massachusetts requires wet vents to be at least 2" in diameter, to be sure there is enough area for both water draining and air venting at the same time. So if the current connection of the combined bathtub/lavatory drain to the stack is a 2" connection, you could rework the drains upstream of that point to take advantage of wet venting.

Cheers, Wayne
 

wwhitney

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P.S. If the existing combined bathtub/lavatory drain to the stack is 1-1/2", then you are going to have to enlarge it to 2" anyway, because it is maxed out for its size and you can't add a shower to it. In the Massachusetts code, a lav is 1 drainage fixture unit (DFU), a bathtub is 2, and a shower is 2. A 1-1/2" horizontal drain can only carry 3 DFUs; a 2" horizontal drain can carry up to 6 DFUs.

Cheers, Wayne
 

Reach4

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If the existing combined bathtub/lavatory drain to the stack is 1-1/2"
How about something like this:
p418-338-2.jpg
https://www.supplyhouse.com/Spears-P418-338-3-PVC-DWV-Sanitary-Tee-w-2-R-and-L-Side-Inlets with bushing down the side ports where needed? Three side inlets, so separate tub and shower and lav inputs. Acceptable? Not what a plumber would do, I suspect.

Dry venting the tub, continues in 2 inch joining the shower, which together join the lav into a 3x3x2 santee would probably be more conventional.
 
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Jian

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P.S. If the existing combined bathtub/lavatory drain to the stack is 1-1/2", then you are going to have to enlarge it to 2" anyway, because it is maxed out for its size and you can't add a shower to it. In the Massachusetts code, a lav is 1 drainage fixture unit (DFU), a bathtub is 2, and a shower is 2. A 1-1/2" horizontal drain can only carry 3 DFUs; a 2" horizontal drain can carry up to 6 DFUs.

Cheers, Wayne

Good point on the DFU! Now enlarging the drain pipe size to 2'' totally makes sense to accommodate the addition of new shower.

Actually if the drain size is increased to 2'', it seems to me that the plumbing layout could be even much easier including not need of the previous vent for tub. Or maybe I am wrong and I should still keep the previous vent either for tub or shower. Below I had a simple draining of the new proposal if the vertical 1-1/2'' dry vent can carry the total DFUs which is 6.
IMG_20201119_203512448.jpg
 
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