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Thread: Shower drain vent question

  1. #1
    DIY Junior Member WendyH's Avatar
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    Default Shower drain vent question

    I thought my DVW plan was all set until I read Terry's response to someone about not having toilet waste washing past a wet vented shower. Hmmm. I'd rather do things right so the system works well without bubbling or siphoning.

    The horizontal run in the space between my 2 upstairs baths is as follows (going downhill)
    1. guest bath WC
    2. new shower drain (runs about 3' to wye)
    3. 3" vent stack to attic and out
    4. Lav drain (has its own vent which shoulders into main vent)
    5. master bath toilet
    6. down turn into waste stack to basement.

    All this takes place in a 6 foot run, so nothing is far from anything. Do I need to add a separate dry vent for the shower drain? Fitting one would be painful but possible using the space under the shower bench to add the upward fitting. From the wall, tying into an existing dry vent going to the main stack would be simple. That said, I don't want to go doing anything unnecessary.

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    Wet venting means you can run a shower or lav into a toilet vent on the same floor.
    You can't run a toilet into a shower vent.
    I would reconfigure and put in the vents. Frankly, you are talking about a few fittings, and then you know it will work.
    I've seen plenty of homeowner and handymen jobs where they didn't understand the physics of it.
    One grumpy homeowner was upset that everytime he drained the soaking tub, black gooey stuff filled his shower.
    And when he dumped his kitchen sink on the other side of the house, the washer downstairs overflowed.
    Handyman plumbing without the vents.
    If you put your thumb on the top of the straw, it doesn't drain.
    Plumbing is the same way. For every pipe going down, you need one going up.
    For every trap, you need to vent it or it will siphon.
    If you are letting water dump down a pipe without a way of air entering the pipe, you will be pushing a cushion of air downwards causing grief downstream.
    A few fittings here would be really cheap insurance. And I think the layout in that tight of space is going to require more mind bending then usual.
    Sometime that a 8,000 hour plumber can do in his sleep.

  3. #3
    DIY Junior Member WendyH's Avatar
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    I'd much rather do things right. The vent will be added. I know I can't use a san-tee on it's back for a drain. Can I use one to branch the vent upward off the horizontal shower drain line? If not, should I use a wye with the arm pointing back toward the trap and then a 45 degree to get it vertical?

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