# Double wye



## luv2plum

.....and another thing. Is dual venting side-by-side lavs with a double wye and two street 45's legal in your area? Here in Ontario it is approved in the building code and is passed by every inspector I've met. But if you're plumbing just one lav, you can't use a wye and fitting 45....it has to be a TY if on the vertical. 

I understand the reasoning of the TY, since a wye and fitting 45 is an S-trap, but then why is that allowed with a double wye?

Can anyone explain this one? So far, countless plumbers, engineers and inspectors that I have quizzed have not been able to answer this one logically, as far as I can tell.


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## swedishcharm21

The trap weir rises above the vent inlet. This increases the chances of self siphonage. You never use a wye or dbl wye in the scenario you described . Sanitary tee, dbl sanitary tee (cross) and up to 2 90's would do just fine. Hope this helps.


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## nhmaster3015

Nope, we can't use a double wye. It puts the trap weir above the inlet


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## plumbdrum

This again?? If you have an issue with it stack your sanitary tee's for a common vent

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## nhmaster3015

These are questions that thirty or so years ago a master would not have to ask. It just shows you how far the trade has fallen and it's not these guys fault either. It is that the current level of education has been deemed acceptable so there is little or no incentive for plumbers to learn any more than they need to get the job passed. What used to be three volumes of text has been reduced to a hundred or so pages.


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## justme

We use what is called a double fixture fitting in Texas, it looks just like a double combo but it is not . Get your pvc fitting book out and you find the fitting I'm talking about.


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## Letterrip

I don't think you guys are answering the right question. He stated that the wye with a st 1/8 is an s trap and can't be used on a single arm. He is wondering why it is allowed in the double lav scenario.


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## tim666

Letterrip said:


> I don't think you guys are answering the right question. He stated that the wye with a st 1/8 is an s trap and can't be used on a single arm. He is wondering why it is allowed in the double lav scenario.


I like it when people actually read the question instead of trying to prove they know more than someone else. I actually didn't realize that they would accept a double y with spigot 45's, I don't think they would in Nova Scotia but then again I never tried.


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## luv2plum

Letterrip said:


> I don't think you guys are answering the right question. He stated that the wye with a st 1/8 is an s trap and can't be used on a single arm. He is wondering why it is allowed in the double lav scenario.


You got it.


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## plumbdrum

I can think of numerous ways of not doing it, so why would you do it to begin with.

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## luv2plum

plumbdrum said:


> I can think of numerous ways of not doing it, so why would you do it to begin with. Sent from my iPhone using PlumbingZone


It's more a question of why is it allowed. I assume there is some rational thought behind this double wye & st45 scenario being allowed, but I just can't understand why. Understanding the reason would help me learn something more, since at the moment it appears to me that this is something that should not be allowed. That being said, it was even shown in the appendix of our code book as a recommended/allowed practice. I am not criticizing it, nor agreeing with it. 

But the "WHY" is what I am after. Does a double wye allow better air movement or transfer? Is there something about the hydraulics of this setup that will not siphon the trap? This is the type of thing I am after. 

I could/would absolutely just do a different way of venting, but why is this one allowed? It is cheaper and easier than the alternatives, so there actually is some incentive to learn why.


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## Dpeckplb

If for example you have two lavs on a 1 1/2 drain. You must use a double wye. It is because a double Ty the flow may flow across into the inlet on the other side. As to the do it differently it may not always work depending on the cabinat.


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## plumbdrum

Sounds to me to be conflicting codes with each other and the easiest but not correct way short of getting the double fixture fitting.

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## JWBII

What exactly is the difference in a combo / TY and a wye+fitting 45 other than obviously one is 2 fittings and the other isn't.

Doesn't make much since to me once so ever to allow one but not the other.

Like justme said though here we use a fig 1 in those scenarios.


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## Ptturner91

luv2plum said:


> .....and another thing. Is dual venting side-by-side lavs with a double wye and two street 45's legal in your area? Here in Ontario it is approved in the building code and is passed by every inspector I've met. But if you're plumbing just one lav, you can't use a wye and fitting 45....it has to be a TY if on the vertical. I understand the reasoning of the TY, since a wye and fitting 45 is an S-trap, but then why is that allowed with a double wye? Can anyone explain this one? So far, countless plumbers, engineers and inspectors that I have quizzed have not been able to answer this one logically, as far as I can tell.


I'm in ontario as well, I made the mistake of posting my urinal rough in with double wyes, got ripped apart on here, but it's allowed in our code 

It is conflicting code, but a long time ago from what I've gathered from older guys is double tees were allowed but they were having problems snaking, it was going straight 
So they banned those 

I really don't know, just know I've passed tons of inspections using that same appendix you are talking about


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## BC73RS

luv2plum said:


> .....and another thing. Is dual venting side-by-side lavs with a double wye and two street 45's legal in your area? /QUOTE]
> No, absolutely not...and I'm sticking to it. Don't even ask me why.
> 
> 
> Sorry for being so rude, had a few wobbly pops hence The Netherlands won and moved on in the World Cup.
> Tomorrow's another day, carry on...


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## nhmaster3015

At 1/4" per foot grade on the trap arm, just how far can you go with 1-1/2" pipe before the trap weir is above the wye & 1/8th bend inlet? THATS what you need to be concerned about. Here, you can't do it at all if there is a trap involved. I don't know about canada, maybe they don't understand basic plumbing up there. As far as double fixture fittings are concerned, they are nice but not required here either and damn near impossible to get anyway so a double San tee is the preferred fitting and screw the drain cleaner whiners.


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## plumbdrum

nhmaster3015 said:


> At 1/4" per foot grade on the trap arm, just how far can you go with 1-1/2" pipe before the trap weir is above the wye & 1/8th bend inlet? THATS what you need to be concerned about. Here, you can't do it at all if there is a trap involved. I don't know about canada, maybe they don't understand basic plumbing up there. As far as double fixture fittings are concerned, they are nice but not required here either and damn near impossible to get anyway so a double San tee is the preferred fitting and screw the drain cleaner whiners.


Like NH said, just throw a clean out under your sanitary tee and be compliant, then you can relax and eat some Canadian Bacon

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## plbgbiz

plumbdrum said:


> Like NH said, just throw a clean out under your sanitary tee and be compliant, then you can relax and eat some Canadian Bacon Sent from my iPhone using PlumbingZone


 Hah! Canadians wouldn't know bacon if it bit them on their pork loins. :laughing:


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## StL92

S Trap like a Sum-*****


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## canuck92

According to the OPIA website " there are substantial revisions comming in the near future, specificly in the 7.5 venting section" i wonder if this will be one. Rumor has it january 2017 is when its changing again. Perfect just befour i get to write the exam...


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## truckman5000

I do agree..
I do think its hog wash...
Look at a "no-hub" sanitary tee that would be fine to pick up a sink.
Look at a PVC why +st.45 and its the same make up as a no-hub T-why.
Same thing as a "long sweep" 
A PVC L.S 90 is the exact same radiance as a no-hub 90. 
Yes my above isnt "code" but the same thing


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## GAN

Double Wye with street 45, nope.

Double fixture tee, yes, weir is still open.


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## dazedel8

If you use a wye and a street 45 you can only go about 18" before you choke off the vent. Thats all there is to it.


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## dclarke

To me it seems like poor
Interpretation of the code. Being a wye st 45 combo is the exact same pattern as a t wye they should be viewed the same in my eyes. Either way wouldn't meet code here.


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## sparky

A wye and 45 cost way more than a tee or cross,why put more money in a job than necessary


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## Dave C.

they simply allow this double combo in the vertical because they know the cross is wrong,if you cant stack the san. tees on top of each other(which i dont really like)use a fixture fitting its better plumbing than the double combo....


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## HonestPlumb

nhmaster3015 said:


> These are questions that thirty or so years ago a master would not have to ask. It just shows you how far the trade has fallen and it's not these guys fault either. It is that the current level of education has been deemed acceptable so there is little or no incentive for plumbers to learn any more than they need to get the job passed. What used to be three volumes of text has been reduced to a hundred or so pages.


Not in disagreement with you at all, but 35 years ago, I was taught to use a 2" X 1-1/2" Cross Wye with St 45s (1/8 bends) usually DWV copper to keep the "trap adapter" (we called them Desanko fittings) as far back as possible. When roughing for back to back Pedestal Sinks. Back then the tolerances on drain heights of Pedestals were limited. The porcelain on the back of the pedestals cam up, and they were "U" shaped for the trap to sit in. Even just a couple inches screwed you, either being to high or to low. If you had one on top of the other coming out for a back to back. So, inspectors OK'd the cross wye's. Being that it was a 2" drain, there was never a problem with siphoning of the other trap, when dumping a full basin. Was so glad to see them do away with the porcelain coming up the back ! Especially when the show room "salesperson", would give you the roughing dimensions for a oddball Pedestal from France, that was hand painted, and the usable part of the bowl was 9" in diameter !! Of course the dimension they wound up giving you was not the correct one ! :furious: After the that happened a couple times, the sink was on the job, before I roughed it in !!! There was no pulling the Pedestal base out of the way to snake it like now a days either. Back then, they always had a nice big lip on the bottom of the basin, that the Pedestal base sat behind.


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## ShtRnsdownhill

HonestPlumb said:


> Not in disagreement with you at all, but 35 years ago, I was taught to use a 2" X 1-1/2" Cross Wye with St 45s (1/8 bends) usually DWV copper to keep the "trap adapter" (we called them Desanko fittings) as far back as possible. When roughing for back to back Pedestal Sinks. Back then the tolerances on drain heights of Pedestals were limited. The porcelain on the back of the pedestals cam up, and they were "U" shaped for the trap to sit in. Even just a couple inches screwed you, either being to high or to low. If you had one on top of the other coming out for a back to back. So, inspectors OK'd the cross wye's. Being that it was a 2" drain, there was never a problem with siphoning of the other trap, when dumping a full basin. Was so glad to see them do away with the porcelain coming up the back ! Especially when the show room "salesperson", would give you the roughing dimensions for a oddball Pedestal from France, that was hand painted, and the usable part of the bowl was 9" in diameter !! Of course the dimension they wound up giving you was not the correct one ! :furious: After the that happened a couple times, the sink was on the job, before I roughed it in !!! There was no pulling the Pedestal base out of the way to snake it like now a days either. Back then, they always had a nice big lip on the bottom of the basin, that the Pedestal base sat behind.


ah you are so correct..I remember guarding my kohler rough in books with a big hammer..LOL..if you lost it try and find another..and then of course the customer would change the sink or fixture just after the tile went up...now most of the pedestals are open in the back from the floor up to the sink..most if not all the pedestal sinks came with wall brackets to hand the sink on and then just lift up the front and slide the pedestal under the sink...


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## A Good Plumber

luv2plum said:


> .....and another thing. Is dual venting side-by-side lavs with a double wye and two street 45's legal in your area? Here in Ontario it is approved in the building code and is passed by every inspector I've met. But if you're plumbing just one lav, you can't use a wye and fitting 45....it has to be a TY if on the vertical.
> 
> I understand the reasoning of the TY, since a wye and fitting 45 is an S-trap, but then why is that allowed with a double wye?
> 
> Can anyone explain this one? So far, countless plumbers, engineers and inspectors that I have quizzed have not been able to answer this one logically, as far as I can tell.



I agree that the relation of the weir of the trap to the start of the vent is the reason why the wye and 1/8th bend should not be legal, but I gotta think that in the case of a double fixture, your local code has forgiven this technicality in favor of being able to allow a cable to get through the trap 
arms and down the waste riser. 
Just a thought, but if i was snaking the trap arms I would be glad the double wye was there, right or wrong.


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## GAN

Any fitting that does not cut off the Hydraulic gradient in a horizontal to vertical change of direction. So a cross tee with a CO above it would pass in Illinois.

Where a T-Wye with no extensions would work and a double wye would not in any case. Some municipalities may go ahead and pass them even though it is a code violation.


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## ShtRnsdownhill

if you used a double Y with 45s, you would have to T above and bring the vents back down, alot of work just to worry about being able to snake a possible clogged drain..now if you had extended runs , past code for the arms, then you have to bring a vent over anyway...


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## plumbdrum

The fact that this topic needs to be explained baffles me.


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## ShtRnsdownhill

I think more of just hashing if using different fittings and making them work( to code), than why a fitting wont work( theory of it)...I just use a double TY and dont worry about if it might clog 20 years down the road...but thats just me....if plumbed out correctly with PVC, the chance of a clog is a very low %....


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## wyrickmech

A single wye is ok but we never use a double. Company policy


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## mtfallsmikey

Color me stoopid, but for the other geezers on here (other than me), wasn't that method allowed under the old CABO code?


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## JohnnieSqueeze

A Good Plumber said:


> I agree that the relation of the weir of the trap to the start of the vent is the reason why the wye and 1/8th bend should not be legal, but I gotta think that in the case of a double fixture, your local code has forgiven this technicality in favor of being able to allow a cable to get through the trap
> 
> arms and down the waste riser.
> 
> Just a thought, but if i was snaking the trap arms I would be glad the double wye was there, right or wrong.




I was told a story about an apartment drain snaking of lavatory the snake went through the double san tee into the other apartment, tennant was out of town, basically demolished the bath, ripped the curtain down towel bars medicine cabinet broke holes and tears all over the place.


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## JohnnieSqueeze

ShtRnsdownhill said:


> if you used a double Y with 45s, you would have to T above and bring the vents back down, alot of work just to worry about being able to snake a possible clogged drain..now if you had extended runs , past code for the arms, then you have to bring a vent over anyway...




How about a cleanout 6" below the double san tee


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## JohnnieSqueeze

Double y in the horizontal with two risers santee each one for lav tie back together for vent.


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## mtfallsmikey

JohnsonPlumbing said:


> How about a cleanout 6" below the double san tee


 That would have been fantastic on the sinks in my buildings, but due to "value engineering" wasn't done. It's a challenge to fish a cable down those double tees.


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## GAN

JohnsonPlumbing said:


> How about a cleanout 6" below the double san tee


How about "above" the tee so you can flush the line. Stack a str. tee on top of a regular tee, split the difference in elevation, problem solved.


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## MDservices

Double TY is permitted here and inspectors pass it but to me, a double wye or ty never makes sense. You have to think about the future and about the guy who's going to unblock the drain after you've built the plumbing. So many ways to properly vent without building a double TY... I never have and never will install a double ty or a double wye unless it's for a vent pipe only... even then, the cost of having those select few fittings if and when.. not worth it. Any double TY used needs to have a separate access point higher up to pass a fish because if not, how do you get it down the drain? It's possible but it's not fun.


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## HonestPlumb

*Cross Y-*



ShtRnsdownhill said:


> I think more of just hashing if using different fittings and making them work( to code), than why a fitting wont work( theory of it)...I just use a double TY and dont worry about if it might clog 20 years down the road...but thats just me....if plumbed out correctly with PVC, the chance of a clog is a very low %....


My shop has been using cross Y's with st 45's for 35 years, in every town and city within 30 miles. Never failed inspection one time. The fact that "when", not if the drain stops up, because the kids threw, God knows what down there, is more of a plus to have the snake be able to go down the first time. As opposed to the issue of not only the snake going across 28 times, but of the weir being slightly above the vent. Where a siphon problem has never been an issue in all the years. The idea of having a Clean Out Tee above a Cross Tee, is the most logical, and stays within code.
We all have our different methods we have been taught, through the years. The small variations that are not truly critical to safety, are not even worth the amount of time and space given to something such as this.


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