Connecting a 1.5in vent (vertical) to a 2in drain (horizontal sloping at 1/4in per foot).

Can the fitting be a sanitary tee, or does it have to be a long sweep combo tee?

  • 1
    Anecdotally I've heard that some inspectors will pass that for a dry vent connection, only. I'm not aware of code actually sanctioning that, however. So, ask your local inspection office. Ive also heard of people being forced to rip them out and replace to pass inspection.
    – Ecnerwal
    Commented Jan 29, 2023 at 4:43
  • 1
    ICC allows it, see 706.3Installation of fittings - codes.iccsafe.org/s/IPC2015_NY/chapter-7-sanitary-drainage/…
    – Max
    Commented Jan 29, 2023 at 5:35
  • However, I cannot find the code section for IBC.
    – Max
    Commented Jan 29, 2023 at 5:35
  • @Ruskes a "dry vent" is a vent -- the "V" in DWV -- that never has drain water in it. (It might have rain water, that falls in the top.) When a drain gets a surge of water, like from flushing a toilet, it pulls air. The vent helps prevent a vacuum from forming. Ask the Duck for lots more info.
    – aghast
    Commented Jan 29, 2023 at 17:39
  • 1
    "long sweep is not allowed on a trapped fixture drain" Oh wow, that's new to me (not that there's ever enough space that you'd want to). "Short radius fittings are required to connect individual fixture trap arms to vertical drain and vent piping. Short radius fittings may be used in the drain piping for an individual fixture. Short radius fittings shall not be used in drain piping serving two or more fixtures. Short radius fittings shall not be used at the base of drain stacks. Short radius fittings may be used in vent piping." up.codes/s/uses-for-drainage-fittings
    – Mazura
    Commented Jan 29, 2023 at 19:04

2 Answers 2


The sanitary tee ensures there is venting of the horizontal section even if it is near full. The small bend in the arm is mostly for directing an auger when cleaning out, and is kept minimal to ensure continual venting.

Using a Wye or long sweep here may possibly choke out the venting, which is why they should not be used here.

The long sweep Tee is required at a vertical to horizontal transition, where the drain velocity is high due to the fall. Using a sanitary connection here may cause backup in the vertical feed, and backup in the other, horizontal, feed leg of the Tee.

The long sweep T is not allowed on a trapped fixture drain (from trap, horizontal to vertical). It's ok on a vented branch.

enter image description here

Ref: https://codes.iccsafe.org/s/IPC2015_NY/chapter-7-sanitary-drainage/IPC2015-Ch07-Sec706.3#IPC2015_Ch09_Sec905.3

See also

enter image description here

Ref: https://up.codes/s/uses-for-drainage-fittings

Inspector's may differ in opinion.

  • 1
    The link from Max in comments to question suggests that the sanitary tee is not only permitted but is the correct way to do this. Figure 706.3(8), upper left case. In addition to the reasons in this answer, the sanitary tee is not exactly a tee, itsside port is at 91.2 degrees, allowing for a perfect connection from a 1/4 inch per foot sloping pipe.
    – jay613
    Commented Jan 29, 2023 at 17:56
  • 1
    This is illustrating normal accepted use of a Sanitary tee into a vertical drain. The question is about using a sanitary tee "on its back" for a vertical vent into a horizontal drain.
    – Ecnerwal
    Commented Jan 29, 2023 at 23:04
  • Awesome answers team! Thank you very much.
    – Max
    Commented Jan 30, 2023 at 4:05


  • The inspector requested to upgrade the santees to long sweeps.
  • The reason provided was that a Santee cannot be placed on its back, it has to be up right.
  • Location is California.
  • I haven't found the section of the International Building Code and Uniform Plumbing Code that validates the inspector reason.
  • As indicated above on this thread, the International Code Council and the International Plumbing Code allow a santee to be placed on its back. Which contradict what my local inspector advised me to do.
  • I called the city to ask, the Building Inspector Supervisor mentioned that a long sweep was not ok and that I should be using a Santee after sending my research and feedback from this post.
  • 1
    Maybe politely ask the inspector for the code reference. Don't indicate to him that you're challenging his knowledge or authority, indicate that you just want to learn.
    – FreeMan
    Commented Feb 8, 2023 at 17:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.