I am wondering if someone can weigh in on the use of sanitary Ts or other types of Ts (non-comboYs) in conjunction with AAVs on small bathroom sinks. If we turn to Table 706.3, it seems clear that a sanitary T cannot be used for a horizontal to horizontal or a vertical to horizontal transition. And yet, all AAV manufacturers publish a picture like this: enter image description here

This seems like a violation as the sani-T is on its back, but the use is so pervasive and being suggested by the manufacturers themselves, it makes me think I am not interpreting the code correctly. Does this not count as a transition? Is there an exception?


You're are quoting chapter 7 with the table you provided but chapter 7 is titled "Connections Between Drainage Piping and Fittings". I'd think Chapter 9, Vents, would apply here instead. Chapter 9 doesn't have a list of prohibited fittings that I could find, but does specify size of pipe and distance and placement of the vent connection. As long as you follow those guidelines I think you are good. (Also, UPC explicitly allows a Sanitary Tee to be used to connect a vent to a horizontal drain line and most would say is the more stringent standard)

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The reason the plumbing code does not want the SanT on its back is because it does not direct the flow on down the line. When drain water meets a combination fitting or a 'Y' fitting in conjunction with a 45* bend the contents are not only dropped into the main line but are, with the benefit of force of gravity, driven into and in the direction of the flow. This will actually enhance the overall drainage flow. The main flow actually can get a boost from the branch as moves to its final destiny. The solids that are dropped into a sanT are simply dropped on to the 'floor' of the main line. They can go splat and tend to get stuck there in place. This will impede the flow in the main line. Eventually this can result in a clogged line. However it is OK to install the SanT on its back in the dry venting part of the system. Nothing to go splat. Nothing to clog. Regarding the mechanical vent being install on a SanT, even though it is installed in the drainage part of the system. Nothing is dropped into the main line. Nothing to get stuck. No clogs. No problem.

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  • This makes complete sense to me and I can really appreciate the rational approach. I totally agree with what you are saying that it wouldn't be an issue, but would it still technically be a violation? I just want to know that I am breaking the rules as I break them. – Murenrb Oct 23 '17 at 13:56
  • Support for Paul's comment: ncwhomeinspections.com/Sanitary+Tees,+Wyes+and+Sanitary+Combos – Jim Stewart Oct 23 '17 at 15:00
  • @Jim and Paul, again, I totally agree with the argument. It makes complete sense. The question is: Is this to code? Or is it technically a violation? – Murenrb Oct 23 '17 at 17:51

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