Incorrect use of sanitary tees in drainage systems is a common problem. What is their proper use in plumbing DWV piping? Table 706.3 of the IPC provides code requirements for the proper use of these plumbing fittings.
The branch connection in sanitary tees has a short radius. They can only be used to change the direction of drainage flow in the horizontal-to-vertical orientations. They cannot be used to change the direction of drainage flow in a vertical-to-horizontal direction or a horizontal-to-horizontal direction.
As shown above, the tee lying on its back can be used for a dry vent. In this orientation, the branch connection cannot receive drainage flow because it would be a vertical-to-horizontal change in direction, which is prohibited.
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