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I have this existing cast iron drain pipe. enter image description here

I'm replacing it with PVC. I don't like that it's a tee fitting because that makes it difficult to snake as it can go from one side to the other.

If I put a double wye here, then I might have a siphoning problem because the trap weir will likely be higher than the vent.

Can I put one sanitary tee right above another? My thought was to put a sanitary tee in (3x3x1.5) for the washing machine. Then right below that, I would put another sanitary tee in for the bathroom sink. I have the ability to raise the drain pipe for the washing machine, so that shouldn't be a problem. Seems like it would be a good middle ground. I wouldn't have to worry about the issue with snaking like I do now and no siphoning issue with a double wye.

Thanks in advance.

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    I can't give you code validity, but I know it will work. For the last 30 years, I've had a 3" main stack with a 3x3x2" Sani-T draining the kitchen sink, dishwasher & bath vanity directly above a second 3x3x2" Sani-T draining the washing machine & tub.
    – FreeMan
    Dec 1, 2023 at 18:43

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Yes.

There should be no issue with stacking two sanitary tees here. I would arrange it with the lower one being a 3 x 2 sanitary tee to pick up the washing machine (2" is now standard for washing machines) and on top a 3 x 1-1/2 for the bathroom sink.

Note that you cannot use a double wye in this application, as it would invalidate the vent.

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  • Me, I run every drain at 2" until the trap adapter. Exceeds code, but that's cool. Saves on ever having to get a snake out in the first place.
    – Ecnerwal
    Dec 1, 2023 at 20:03

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