If a PVC tee is used to drain, where the flow of fluid is descending, it is obvious it should be positioned (T pedestal slightly pointing) upwards.

But if the piping segment is used only to vent, with air streaming upwards, should the tee be installed upside down so that the pedestal directions matches the ascending flow of air?

  • 1
    What is "pedestal or pedestal directions" What kind of PVC tee? What else interacts with the tee? What are you trying to do? What is the problem you are trying to solve?
    – Alaska Man
    Jul 26, 2020 at 17:42
  • Pedestal is the one of the three prongs of a tee that doesn't have another one directly opposite to it
    – amphibient
    Jul 26, 2020 at 17:44
  • Prongs? you mean openings? Meaning the opening that is at 90 degrees to the other two. OK. That is usually the inlet receiving the waste from the fixture and the lower one is the outlet to drain and the upper one is for the vent. What else interacts with the tee? What are you trying to do? What is the problem you are trying to solve?
    – Alaska Man
    Jul 26, 2020 at 17:52
  • Yes, opening but in a normal tee, it is not 90°, more like 85
    – amphibient
    Jul 26, 2020 at 17:53
  • Unless you provide more details about what your problem is or why you want to install a tee (incorrectly?) on its side then we can not try to help you. Upside down? Vent tee, not sanitary tee? Describe, in detail, the venting you are trying to do please.
    – Alaska Man
    Jul 26, 2020 at 18:03

1 Answer 1


If you are using a sanitary tee to go from a horizontal vent pipe into a vertical vent the correct orientation is "upside down" from its normal usage. The curve of the tee should go from the horizontal direction curving up toward the roof. Air flows into the vent from outside to replace air pushed downstream by the falling waste, so the vent is oriented to allow smooth airflow from the roof side into the horizontal vent. sanitary tee in upside down orientation

  • 1
    This exactly answers my question, which apparently is not as obscurely formulated as suggested in the comments above
    – amphibient
    Jul 26, 2020 at 18:42
  • Does it make a difference if the vertical stack is a wet vent? I'm still using the horizontal pipe strictly for venting. Feb 22, 2022 at 13:08
  • For reference, you can find this answer in the 2015 International Plumbing Code (3rd Printing as adopted by New York State) in Figure 706.3(10) PROPER USE OF DWV-PVC/ABS 90-DEGREE FITTINGS. codes.iccsafe.org/s/IPC2015_NY/chapter-7-sanitary-drainage/…
    – dossy
    Sep 7, 2023 at 15:21

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