Cross over flow in back to back toilets- solution? Can

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tfoster115

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I have read the other threads so I know the problem. We bought a house a year ago built in 1970's. We did check the plumbing when we bought to make sure everything flushed and drained. We remodeled first the master and just now the guest bath. We installed new toilets without knowing the issue they have with a sani cross t. We did consult a reputable plumbing company before we installed the new guest toilet and mentioned we had heard gurgling and wanted to know if it was a design issue. He is who mentioned the cross in the cast iron but never said it was an issue- just made comment that because of the cross his camera would not be able to be sent from the toilet into the line. (We had pulled the old toilet so I thought it would be easy to access from there)

Now with the new toilets in both bathrooms we have the issues described about the syphon, the bubbling and yes the surprise bidet treatment you get if sitting on toilet when other is flushed. Our plumbing is below the slab so removing the cross I don't see being affordable or easy. I know that is the ultimate solution. But I want to know if any of you experienced guys have come up with a work around that would reduce symptoms we are having. The toilets are on the end of the house at the beginning of the run so maybe tunneling in and cutting out the old cross won't be a huge expense but it seems like it would be. No, jackhammering my slab isn't really an option since we just laid new floor and tile in both bathrooms. Yes, I have since learned on any future remodel of a house and back to back fixtures this will be addressed up front.
 

Tuttles Revenge

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I haven't had any customers complain about that issue myself.. But I know that I'm looking at a remodel project tomorrow with existing back to back toilets that I will absolutely be addressing..

I had started to draft a reply to this on Friday before I left the office, but the dog wasn't patient enough to let me finish..

But I wonder if a baffle could be installed from above into the tee that could prevent the cross/jump over of a flush of water?
 

tfoster115

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I haven't had any customers complain about that issue myself.. But I know that I'm looking at a remodel project tomorrow with existing back to back toilets that I will absolutely be addressing..

I had started to draft a reply to this on friday before I left the office, but the dog wasn't patient enough to let me finish..

But I wonder if a baffle could be installed from above into the tee that could prevent the cross/jump over of a flush of water?
Let me know what you found when you looked at the remodel project. If the t is under the slab how would we go about installing the baffle? Without jackhammer to the floor to reach the t.
 

Jeff H Young

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I haven't had any customers complain about that issue myself.. But I know that I'm looking at a remodel project tomorrow with existing back to back toilets that I will absolutely be addressing..

I had started to draft a reply to this on Friday before I left the office, but the dog wasn't patient enough to let me finish..

But I wonder if a baffle could be installed from above into the tee that could prevent the cross/jump over of a flush of water?
Good Idea like a BW valve? it would need a certain access haven't heard of anything like that before .
 

Tuttles Revenge

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Good Idea like a BW valve? it would need a certain access haven't heard of anything like that before .
I'm thinking more like how a kitchen sink center outlet continuous waste has a baffle to keep each side of each sink going down rather than across the tee.
 

Jeff H Young

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I'm thinking more like how a kitchen sink center outlet continuous waste has a baffle to keep each side of each sink going down rather than across the tee.
yea and its easy to take a tubular fitting apart. generally I think restrictions are prohibited but not sure
 

Tuttles Revenge

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yea and its easy to take a tubular fitting apart. generally I think restrictions are prohibited but not sure
I think a well designed baffle might not create a real restriction. And so long as it had a maintenance port via the vent.

In the end, which is worse, sewer gasses entering a home or a baffle installed in a san cross that can't be removed due to structural conditions?

My upcoming project has this San Cross installed currently and they are planning on only remodeling 1 of the bathrooms. It probably has 1.6gpf toilets installed currently but in order to not get call backs due to the potential of the crossover flush syndrome, we will be removing this fitting and replacing it with a fitting that prevents that issue... but now which fitting to use?

San Cross.jpg
 

Terry

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If at all possible, consider bring up a second drain for the other toilet. You could wye off below for the second one, and the single vent should be enough for both.
So a santee for one, and wye off below for the second one.
 

wwhitney

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If you need to use a double fitting, then double combination, for sure.

One could imagine a 4x4x3x3 double san-tee or fixture fitting which had a baffle for maybe 2-4" of height splitting the 4" barrel in between the two side inlets. (4/3) squared is almost 2, so it wouldn't be much of an obstruction.

Or if a 4x3x3 inline wye existed (one end a 4" outlet, the opposite end two 3" inlets pretty close to each other, then two 3" san-tees and two of those fittings would give good separation.

But none of these are retrofittable, I can't think of a way to remediate an existing below slab double san-tee like the OP has, short of replacing it.

Cheers, Wayne
 

John Gayewski

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I think a well designed baffle might not create a real restriction. And so long as it had a maintenance port via the vent.

In the end, which is worse, sewer gasses entering a home or a baffle installed in a san cross that can't be removed due to structural conditions?

My upcoming project has this San Cross installed currently and they are planning on only remodeling 1 of the bathrooms. It probably has 1.6gpf toilets installed currently but in order to not get call backs due to the potential of the crossover flush syndrome, we will be removing this fitting and replacing it with a fitting that prevents that issue... but now which fitting to use?

View attachment 82047
Iapmo figured 5 wil probably be the only one of the two options that fit.
 

Tuttles Revenge

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OK.. another twist in this sorrid tale. We have a project starting today where we are taking out one of the back to back toilets and moving it roughly 10ft away around a couple 90° bends and picking up a shower and lav in between in a horizontal wet vented system. Ideally we will be utilizing the same connection to the stack (tho probably changing out the double san tee fitting. I wonder if the same problem would occur if one toilet is in that existing back to back configuration while the other is further but on the same san tee. But it seems that with a bit of distance the effect should be mitigated.

I need to build this setup in the parking lot and do some testing..
 

wwhitney

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The far WC should not wash across to the near WC at all. The near WC could wash across the double san-tee but presumably not past the first bend (going upstream). Not sure if that would negatively impact the flow of, say, a contemporaneous shower.

Cheers, Wayne
 

Terry

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I will bet money that if the double cross is left in, then yes, as the new toilets are flushed, it's skipping across, pushing a column of air ahead of it, and displacing water in the opposing bowl.
 

Tuttles Revenge

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The far WC should not wash across to the near WC at all. The near WC could wash across the double san-tee but presumably not past the first bend (going upstream). Not sure if that would negatively impact the flow of, say, a contemporaneous shower.

Cheers, Wayne
That is what I was thinking too. We completely changed the rough in design today due to several heating ducts in the way. We removed the double san tee and installed 2 san tees stacked.
 
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