Back to back toilet diagram

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Kurtr12

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I have a back to back toilet installation from a house built in the 70’s. After replacing the toilets I encountered the water skipping problem from one toilet to another. I switched from 3 inch to 2 inch valve toilets, but I’m still tired of one toilet getting drained, even when it’s better than when it was 3 inch valve toilets. My drain lines run horizontally and I’ve attached pictures of all of the connections so you can take a look at what I’m dealing with. I’m trying to avoid cutting out and redoing structure to fit in the double combination wye with the 1/8 bend. Would my diagram I made work? The old setup is on the left and the new proposed connections are on the right. I’ve attached pictures of all the venting and existing connections. Let me know if you need more info.
 

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  • 3 inch vent.jpg
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wwhitney

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What fixtures are draining in from the left, and how are they vented? Moving the 1.5" vent upstream like that may or may not be appropriate.

On the drainage side, a horizontal double wye will certainly work better than the existing horizontal double san-tee. The existing fitting is a terrible choice, because both inlet are inline, and so best case they are both flat with no slope. For the same reason you'd never use a one piece double combo horizontally. With the double wye, the branch inlets are still at less somewhat sloped, and you can rotate each of the 45s to have 2% slope on the inlet.

Whether the change will completely fix your crossover problem, I'm not sure

Cheers, Wayne
 

Kurtr12

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What fixtures are draining in from the left, and how are they vented? Moving the 1.5" vent upstream like that may or may not be appropriate.

On the drainage side, a horizontal double wye will certainly work better than the existing horizontal double san-tee. The existing fitting is a terrible choice, because both inlet are inline, and so best case they are both flat with no slope. For the same reason you'd never use a one piece double combo horizontally. With the double wye, the branch inlets are still at less somewhat sloped, and you can rotate each of the 45s to have 2% slope on the inlet.

Whether the change will completely fix your crossover problem, I'm not sure

Cheers, Wayne
There is a bath tub and shower to the left. Attached is a picture of the vents from when I demoed the bathroom years ago.
 

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