Properly venting a toilet underslab, help please!

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by Arya Ebrahimi, Jun 25, 2014.

  1. Arya Ebrahimi

    Arya Ebrahimi New Member

    Messages:
    7
    Location:
    West Virginia
    Good evening all, I've been reading and searching here till I'm blue in the face, and now I have some questions.

    I am building a house in WV where there are no building or plumbing codes/permits/inspections. This is great because it's less headaches, but it would be nice to have someone check my work over before I pour the slab. :)

    My major question/concern is how to vent toilets underslab. I have read that santee's are basically not to be used underground, although I have seen them in several reference materials posted on this forum. I have also read where flat venting is not allowed either.

    In the picture below, would the venting method be acceptable if the san tee were a wye/45 combo? Basically an elbow from the main up to a 3x3x2 wye to the closet flange? I didn't have a wye of that size on hand for mockup.

    20140625_183309[1].jpg

    The other way I came up with would be to roll a wye off the main after the toilet, but it would result in a flat vent for about 2 feet.

    20140625_182928[1].jpg
  2. Terry

    Terry Administrator Staff Member

    Messages:
    14,780
    Location:
    Bothell, Washington
    The vertical wye works fine.

    Also, if the rolled wye was also for a lav drain, with cleanout, it would be considered wet.
    You can wet vent the toilet with a nearby lav. (If it's done right)
  3. Arya Ebrahimi

    Arya Ebrahimi New Member

    Messages:
    7
    Location:
    West Virginia
    Thanks Terry, I was hoping this would work.

    I'm striving to vent every fixture as it seems to be a fool proof way to eliminate "gremlins" in the system, and it's really not a huge cost.

    With regard to your second comment, how and where are cleanouts accomplished in underslab environments? I specifically laid out my underslab mains to end at toilets, so that the closet flange could be used as a cleanout if necessary. Are the cleanouts for other things such as lavs, installed in the vanity? And what about tubs, I don't think I've ever seen a cleanout on a tub drain? It's completely buried under the tub/concrete. How would you facilitate a cleanout in that condition?

    I'm interested in doing this the right way the first time, and want to make sure I don't screw anything up. I've been in construction for 15 years, but have never really designed/installed a DWV system until now. This forum has been invaluable!
    Last edited: Jun 25, 2014
  4. Terry

    Terry Administrator Staff Member

    Messages:
    14,780
    Location:
    Bothell, Washington
    A line within five feet of a line with a cleanout is okay. If you have a line though the home, and you add fixtures near that line, you may be able to keep them within that distance.
    Most tubs get by for that reason without an added cleanout.

    Where is the lav in that room?
  5. Arya Ebrahimi

    Arya Ebrahimi New Member

    Messages:
    7
    Location:
    West Virginia
    Terry, here is the overall layout of the first floor. The blue lines are my mains/branches. The green lines indicated my vents. I know the green lines can be a bit hard to see, but they're there.

    overall plumbing diagram.jpg

    The bathroom in question is the one on the left of the image, although I have similar things happening on the right as well.

    The lav could very well be tied into a rolled wye, although I was planning on just running a 3x3x2 wye flat and venting the toilet independently.

    Thanks for your help.
  6. Terry

    Terry Administrator Staff Member

    Messages:
    14,780
    Location:
    Bothell, Washington
    You would be better off venting with the lav. It also gives you a way to snake the "vent", as its also a drain line for the lav.
    It's also fewer fittings and pipe. Bonus! :)
  7. Arya Ebrahimi

    Arya Ebrahimi New Member

    Messages:
    7
    Location:
    West Virginia
    If I am going to wet vent the toilet through the lav, does the wye that ties the lav drain to the main have to be rolled? I understand it is good practice, but I am at the shallow end of the house and don't have enough vertical room for a rolled wye configuration without projecting up into the slab.

    For reference, the tub drain has a dedicated vent that is within 7' of the lav drain connection to the main, and 9' of the closet flange.
  8. Arya Ebrahimi

    Arya Ebrahimi New Member

    Messages:
    7
    Location:
    West Virginia
    Well, this is where I ended up. Hopefully it passes muster.

    20140626_205802[1].jpg

    Lav is the branch on the left, tub is the branch on the right with a dedicated dry vent, and water closet is in the center.

    Please let me know what if anything needs to be changed.

    Thanks for your help!

    Ary
  9. Terry

    Terry Administrator Staff Member

    Messages:
    14,780
    Location:
    Bothell, Washington
    The toilet and lav are fine. However an inspector here would have made me run 3" to the lav with an end of run cleanout. You can still pull the toilet if you need to snake the line.

    The tub vent should be a wye or combo straight up into a wall. If the line had run with the wall, the vent come have come straight up into it.
  10. Arya Ebrahimi

    Arya Ebrahimi New Member

    Messages:
    7
    Location:
    West Virginia
    Terry, thanks for helping me through this.

    Is the reason for your suggestion on the wye/combo because I have a "flat vent" for approximately 1'? Is this a huge concern? I must admit I have not really understood why flat venting is wrong, although I have tried to avoid it as much as possible. In the case of the tub, I figured having the drain flow straight towards the main instead of having 2 90s to run it under the wall would be better.
  11. Terry

    Terry Administrator Staff Member

    Messages:
    14,780
    Location:
    Bothell, Washington
    If the line plugs up, it submerges the drain line, which can fill with goo. Unless you have a cleanout on the vent, it stays gooed up.
    The wye headed to the tub could have been position so that you only had one 45 on that line.
  12. Arya Ebrahimi

    Arya Ebrahimi New Member

    Messages:
    7
    Location:
    West Virginia
    I can visualize the layout in my head now. For this one, I think I will just put a cleanout on the vent since I highly doubt it will ever get backed up, and if it does there's an easy access point for a cleanout anyway.

    I will do my best to get the next one right. Is it bad practice to put a vent upstream from the last waste line on the run? Basically the tub on the other side of the house is at the end of it's respective run, and I'm trying to figure out the best layout for the trap and vent so that the drain "washes" the vent. Thus far I have been unsuccessful in that attempt, other than to have the drain line go away from the main as it exits the tub and make a u-turn. That would allow me to put the vent downstream from the drain and still get it in the wall without flat venting.

    Any words of wisdom here?
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