# Back to Back Toilets



## bjcrist1234

I have just installed two new Toto toilets and they are back to back. When toilet number one is flushed everything is fine. Flush #2 toilet and it pulls water out of the bowl of #1 toilet. Clear down into the throat of the bowl. Both toilets use the same vent. A misteryto me! Any thoughts?


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## justin

bjcrist1234 said:


> I have just installed two new Toto toilets and they are back to back. When toilet number one is flushed everything is fine. Flush #2 toilet and it pulls water out of the bowl of #1 toilet. Clear down into the throat of the bowl. Both toilets use the same vent. A misteryto me! Any thoughts?


bigger vent . or restricted


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## billy_awesome

You would think if the one toilet worked fine, there wouldn't be a blockage in the vent, what size vent for your dual vent? 1 1/2" for my code, but really a straw could vent some of these low flush toilets.

It might even be a blockage in the one toilet, or maybe a cracked toilet, it's usually something stupid and never crazy atmospheric pressure dilemma.


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## walker426

bjcrist1234 said:


> I have just installed two new Toto toilets and they are back to back. When toilet number one is flushed everything is fine. Flush #2 toilet and it pulls water out of the bowl of #1 toilet. Clear down into the throat of the bowl. Both toilets use the same vent. A misteryto me! Any thoughts?


Are they connected on a double san tee or wye and what is the total center to center distance of pipe


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## MikeS

yeah, wasn't there some discussion about this a little bit back? About the difference between a double sani-tee (which is incorrect) and a double fixture fitting? And how these new toilets on double sanitees have this problem? I just did a back to back toilet repair, but made sure I used a double fixture fitting, even though the supply house wanted to initially give me a double sanitee.


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## LEAD INGOT

If you have a 3" sancross and 3" stack, you have to maintain a minium of 30" center of stack to center of flange. The 30" is to absorb the shock of the higher velocity discharge of the newer toilets. The 30" is code where I'm at, but the science behind it universal.


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## xyleman

I believe that toto wants a double wye as to san t in their lit.


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## Pipecommandor

Two toilets on the same wet vent ???


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## mccmech

Pipecommandor said:


> Two toilets on the same wet vent ???


Who said it's a wet vent? OP only stated that they share a vent, that doesn't mean it's a wet vent.


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## walker426

xyleman said:


> I believe that toto wants a double wye as to san t in their lit.


 Technically there is no correct way to vent a floor mounted toilet this is why a double wye works best no hydraulic jump


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## Redwood

This has been discussed before...


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## PrecisePlumbing

This has probably been discussed before but no such drain arrangement can exist here in oz unless the top of the junction is directly vented eliminating syphonage of the trap. Having a back to back cross wyye is lazy plumbing as far as i am concerned. Stand up and branch it correctly as a separate line with its own stack run


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## NYC Plumber

billy_awesome said:


> You would think if the one toilet worked fine, there wouldn't be a blockage in the vent, what size vent for your dual vent? 1 1/2" for my code, but really a straw could vent some of these low flush toilets.
> 
> It might even be a blockage in the one toilet, or maybe a cracked toilet, it's usually something stupid and never crazy atmospheric pressure dilemma.


Dont say that, you would be suprised, ive seen plenty of atmospheric dilemas...


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## Redwood

NYC Plumber said:


> Dont say that, you would be suprised, ive seen plenty of atmospheric dilemas...


Yep and a sudden large flow rate will bring that to the top every time..
These super toilets flush so fast if you blink you'll miss it... :yes:


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## walker426

PrecisePlumbing said:


> This has probably been discussed before but no such drain arrangement can exist here in oz unless the top of the junction is directly vented eliminating syphonage of the trap. Having a back to back cross wyye is lazy plumbing as far as i am concerned. Stand up and branch it correctly as a separate line with its own stack run


I disagree about the lazy **** .when your in a house with a 3 inch copper stack with back to back in a brass cross with lead bends what would be your non lazy replacement solution?


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## TX MECH PLUMBER

MikeS said:


> yeah, wasn't there some discussion about this a little bit back? About the difference between a double sani-tee (which is incorrect) and a double fixture fitting? And how these new toilets on double sanitees have this problem? I just did a back to back toilet repair, but made sure I used a double fixture fitting, even though the supply house wanted to initially give me a double sanitee.


What's a double fixture fitting ?? If not a San tee


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## justin

TX MECH PLUMBER said:


> What's a double fixture fitting ?? If not a San tee


a double combo


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## justin

bjcrist1234 said:


> I have just installed two new Toto toilets and they are back to back. When toilet number one is flushed everything is fine. Flush #2 toilet and it pulls water out of the bowl of #1 toilet. Clear down into the throat of the bowl. Both toilets use the same vent. A misteryto me! Any thoughts?


dude , you KNOW you are supposed to send pics, right ?


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## Titan Plumbing

TX MECH PLUMBER said:


> What's a double fixture fitting ?? If not a San tee


It's NOT a double combo. It's a Double fixture fitting.


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## PrecisePlumbing

walker426 said:


> I disagree about the lazy **** .when your in a house with a 3 inch copper stack with back to back in a brass cross with lead bends what would be your non lazy replacement solution?


Cut out the cross, install 2 junctions with a 1 metre exclusion zone between them and drop the second toilet into its own mini stack. 3 inch isntt sufficient for more than 1 toilet round here anyway. 4 inch is much more suited


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## Redwood

Titan Plumbing said:


> It's NOT a double combo. It's a Double fixture fitting.


Yep.. there is a difference...


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## justin

Titan Plumbing said:


> It's NOT a double combo. It's a Double fixture fitting.


it is a double combo . its NOT a double wye and 1/8th combination. try holding a 3" combo up to it.


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## Redwood

Double Combo and Double Wye with 1/8 Bends are the same...
The Double Fixture is different...
Note the red line in the two drawings below and how the vent would be affected...


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## justin

Redwood said:


> Double Combo and Double Wye with 1/8 Bends are the same...
> The Double Fixture is different...
> Note the red line in the two drawings below and how the vent would be affected...


foot in mouth


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## Titan Plumbing

Stick a double combo on the vertical for a set of lavs and see if the inspector doesn't turn you down, quick!


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## NYC Plumber

Titan Plumbing said:


> Stick a double combo on the vertical for a set of lavs and see if the inspector doesn't turn you down, quick!


Obviously for lavs and any other fixture other than a wc... For wc's it doest matter... Wc is different you want a siphon and its an s trap right????


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## justin

Titan Plumbing said:


> Stick a double combo on the vertical for a set of lavs and see if the inspector doesn't turn you down, quick!


i was thinking before i spoke . i am taking care of four kids . its hectic. im surprised ghat you know that .. mister " i put santees on there back " or " i tie t&ps into pan lines" both code violations , but your inspector lets you do it.


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## Redwood

NYC Plumber said:


> Obviously for lavs and any other fixture other than a wc... For wc's it doest matter... Wc is different you want a siphon and its an s trap right????


Yes, with a mechanism for trap water replenishment as well...


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## NYC Plumber

Redwood said:


> Yes, with a mechanism for trap water replenishment as well...


Now we are talking!


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## Titan Plumbing

justin said:


> i was thinking before i spoke . i am taking care of four kids . its hectic. im surprised ghat you know that .. mister " i put santees on there back " or " i tie t&ps into pan lines" both code violations , but your inspector lets you do it.


I was arguing practical application vs Code, and all the time I was taking care of SIX kiddos.


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## MikeS

Titan Plumbing said:


> It's NOT a double combo. It's a Double fixture fitting.


 isn't this called a "finger five?" the double combi setup? I think either of these methods would work fine compared to dbl sani-tee, but you have to ask yourself why do they make that DFF. So I'll keep going with those for these situations.


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## Redwood

MikeS said:


> isn't this called a "finger five?" the double combi setup? I think either of these methods would work fine compared to dbl sani-tee, but you have to ask yourself why do they make that DFF. So I'll keep going with those for these situations.


In the case of the back to back toilet the recommendation by Toto and others is to use the double combo or double wye and 1/8 bends. This is because the toilet doesn't need the venting like a sink would because it is an s-trap with trap water replacement in place....

The double lav sinks are p-traps which can and should be vented without any trap water replacement. In this case the double fixture fitting should be used as it will allow venting of both trap arms where a double combo being used would cut off the vent....


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## MikeS

well, regardless of what Toto recommends, I have read that UPC requires DFF. Like I said, I don't think it makes a difference, I believe DFF is the current correct fitting, and dbl sani-tee (cross) is wrong.


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## NYC Plumber

Redwood said:


> In the case of the back to back toilet the recommendation by Toto and others is to use the double combo or double wye and 1/8 bends. This is because the toilet doesn't need the venting like a sink would because it is an s-trap with trap water replacement in place....
> 
> The double lav sinks are p-traps which can and should be vented without any trap water replacement. In this case the double fixture fitting should be used as it will allow venting of both trap arms where a double combo being used would cut off the vent....


I agree 100%.


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## NYC Plumber

MikeS said:


> well, regardless of what Toto recommends, I have read that UPC requires DFF. Like I said, I don't think it makes a difference, I believe DFF is the current correct fitting, and dbl sani-tee (cross) is wrong.


Your right For any fixture other than a wc...
Wc is a special fixture, go with manufacturers recomendations if there are any.


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## jeffreyplumber

Most of us got a pretty good idea how to rough in back to back w/c. 
I think he just put 2 new toilets in an existing building. 
Did you find out how it was plumbed? Did they stack 2 santees Wet vent?
I like to know if you found the exact problem and what you did to solve.


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## Mpls Jay

Redwood said:


> This has been discussed before...


Just found this today at a bar.3 Toto's (Really? at a bar? Hmmm.)
Owner said it sucked from the day they went in. 
The b2b's would siphon out at the opposing toilets flush.
Then enter the sewer gas!
Gonna swap the b2b's for 2 Gerber Vipers. Going to show them this fine post first...
Thanks Redwood!


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## bighutch

yes seen this problem in multi-story, do not use a double san tee. florida code calls for double wye (4x3, with 3 inch street eight bends. split the differants)


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