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?
Can a sanitary tee be used to connect a dry vent to a drain
plumbingplumbing-fixture
Best Answer
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.
Ref: https://codes.iccsafe.org/s/IPC2015_NY/chapter-7-sanitary-drainage/IPC2015-Ch07-Sec706.3#IPC2015_Ch09_Sec905.3
See also
Ref: https://up.codes/s/uses-for-drainage-fittings
Inspector's may differ in opinion.