Back-to-back toilet installation

Jadnashua · Apr 3, 2011

In some places the slab under the toilet was per code. If the floor rotted a bit because of a leak, you had a chance of not falling into the next floor when you sat down! It used to be code in Rochester, NY.

Dlarrivee · Apr 3, 2011

BobL43 said:
And a view from the Other side of the cross fitting

The rubber shown here should be a shielded coupling with a metal wrap on it, those rubber-only ones are meant for direct burial work only.

Sponsor · 2022-01-29T12:20:58-0800

BobL43 · Apr 3, 2011

Maybe it IS a NY thing; I am in

Suffolk cty, NY

BobL43 · Apr 3, 2011

Thanks for the info on the shielded coupling

BobL43 · Apr 4, 2011

I guess when all the walls are open, I should run and tie in a new 2 inch vent line in the new wall 6 inches above the flood line and bring it down into the basement to be ready to use should I need it for the lower down Wye, if that is needed in the main stack? If I need to not use that cross for the new toilet, I can if necessary, after the remodel, remove the toilet and PVC bend there now and put a new flange and 3 inch line from it down to the new 3 inch wye and tie in the 2 inch vent line to it. I don't know if I will be able to test it.............. hey wait! I can buy the new toilet now and test it out before ripping the whole room apart to see how it works. only wasted money would be a wax ring for the test. DUH! If there is a problem, I should see it with a few flushes, and I will know which way to go. Terry, by the way, where can I see that video you mentioned in your post # 4 of page 1 of this thread?

BobL43 · Apr 8, 2011

I found more info on the distance between 2 back to back toiltes

I found the following in the NY State plumbing Code:

706.3 Installation of fittings. Fittings shall be installed to
guide sewage and waste in the direction of flow. Change in direction
shall be made by fittings installed in accordance with
Table 706.3 and Appendix H. Change in direction by combination
fittings, side inlets or increasers shall be installed in accordance
with Table 706.3 and Appendix H based on the pattern of
flow created by the fitting. Double sanitary tee patterns shall
not receive the discharge of back-to-back water closets and fixtures
or appliances with pumping action discharge.
Exception: Back-to-back water closet connections to double
sanitary tees shall be permitted where the horizontal developed
length between the outlet of the water closet and the
connection to the double sanitary tee pattern is 18 inches
(457 mm) or greater.
PLUMBING CODE OF NEW YORK STATE
--------------------------------------------------------------------------------------------------------
Is the double sanitary Tee pattern the same thing as the 3 inch sanitary cross I show in my photo? The distances in my situation definitely exceed 18 inches as I said, and is probalby around 5 or more feet. I am not afraid to do the rip out and reconfiguration of the drain stack and reventing, but I definitley would like to avoid tearing apart the finished wall in the room where the access panel is, down at floor level looking up in the photo showing the 2 toilet bends. The is not a whole lot of room to stand up and work between those 2 walls

BobL43 · May 16, 2011

Tested with Toto Promenade Toilet

I purchased and installed a Toto Promenade on to the white PVC bend in my photos and when the Toto is flushed, there is just very little perceivable movement of water in the bowl of the other toilet behind this one. On a very windy day, I have seen the venturi action of the wind over the 3 inch roof vent causing a similar amount of action in the same bowl. I noticed this over the years, but never paid much attention to it until now.

I removed the Toto after about 5 days of testing without seeing any real negative influence of it on the other toilet. It won't be installed until after the other work ( sheet rock, tile, etc. are done. right now I am working out the drain and venting PVC plumbing details of adding a tub to this half bath to make it a full bathroom and relocating the sink from one wall to to the opposite wall.

AlanaS · Mar 13, 2014

Hi Terry. I have a similar issue along this thread. I recently decided to replace my easily clogged American standard toilet with my dream Toto during my bathroom upgrade. In the process I have discovered three issues, first that I have a sanitary cross with back to back toilets, second that my rough in is about 13.5", and finally that my supply valve is very close to the center line of the drain and low to the floor. My first question is this: I see the water ripple effect of using the Toto with the sanitary cross configuration, but do I really need to care about that? Is this going to result in some trouble down the line? Can I live with it?
I have spent a lot of time on the 14" rough-in thread as well, unfortunately my supply valve would interfere with all the skirted Totos that use the unafit adapter.There is a American Standard cadet pro that would work but also recommends against sanitary cross. I should mention here that I have already crawled under my house twice (the second time to take a picture of the cross but my camera jammed!) and I am seven months pregnant and not feeling financially or in any other way prepared to redo all my plumbing.
If I can't live with the Toto on the sanitary cross, I will replace it with an American standard 14" rough-in (looks like cadet 3 would work without moving the supply valve and no mention in the install notes about issues with back-to-back toilets) and give up my dreams of the Toto toilet. Please advise!!
Thanks.
p.s. both toilets are up against a shared wall so unlike the person who had 5 ft, there is not that much pipe between the two toilets.

Terry · Mar 13, 2014

You can use the 3" flush valve bowls on that, Kohler Class Five, Cadet 3, TOTO, but they will push some water out of the opposing bowls. All of these will do that on a San cross. Not a deal breaker though.

A Cadet 3 14" is a 12" bowl. You might as well just use a 12" bowl, because that's what it is. The only thing they do is make the tank a little deeper to the wall. You won't pick up any floor space in front.

Jadnashua · Mar 13, 2014

Dahl sells a 90-degree offset valve, but I might just consider moving the supply line.

As said, most any of the modern low-flush toilets create a much higher velocity water flow, and without the proper fitting, can make for issues. Probably the worst in those, though, might be a pressure assist, which adds a bit more velocity to it.

I'd probably do what was necessary to get a Toto to fit, but that's me.

BobL43 · Mar 13, 2014

AlanaS said:
Hi Terry. I have a similar issue along this thread. I recently decided to replace my easily clogged American standard toilet with my dream Toto during my bathroom upgrade. In the process I have discovered three issues, first that I have a sanitary cross with back to back toilets, second that my rough in is about 13.5", and finally that my supply valve is very close to the center line of the drain and low to the floor. My first question is this: I see the water ripple effect of using the Toto with the sanitary cross configuration, but do I really need to care about that? Is this going to result in some trouble down the line? Can I live with it?
I have spent a lot of time on the 14" rough-in thread as well, unfortunately my supply valve would interfere with all the skirted Totos that use the unafit adapter.There is a American Standard cadet pro that would work but also recommends against sanitary cross. I should mention here that I have already crawled under my house twice (the second time to take a picture of the cross but my camera jammed!) and I am seven months pregnant and not feeling financially or in any other way prepared to redo all my plumbing.
If I can't live with the Toto on the sanitary cross, I will replace it with an American standard 14" rough-in (looks like cadet 3 would work without moving the supply valve and no mention in the install notes about issues with back-to-back toilets) and give up my dreams of the Toto toilet. Please advise!!
Thanks.
p.s. both toilets are up against a shared wall so unlike the person who had 5 ft, there is not that much pipe between the two toilets.

Well, it's almost 3 years now since I did the renovation. The Cross tee is till there, and we never had any problem with water surging up into the Eljer toilet from the Toto toilet.

AlanaS · Mar 13, 2014

Thanks to you all for your responses. I am glad to hear I can just live with what I have for now (and learn not to see the gap between the toilet and the wall).

ram1414 · Mar 19, 2019

Running into the same situation - older home from 50's with back to back Double Sanitary Tee (4")

Question: Is there a distance between toilets and double sanitary Tee that would cause this to be OK? If I moved one of the toilets by 4.5 feet let's say, away from the tee - would that work?

Back-to-back toilet installation

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