I'm looking at tapping into an existing drain line at the vertical vent, which I understand should be via a horizontal run to a sanitary tee. The vent is 2 inch PVC; the horizontal piece I will install is 2 inch PVC.

But what makes a tee "sanitary?" Everything I can find emphasizes the correct usage of tees vs. wyes instead. Fair enough, but how can I recognize the correct tee?

Specifically, I think I grabbed an equal tee(?) instead — how can I recognize whether I have the right part?

  • 1
    To understand why you shouldn't use an equal tee where a sanitary tee is called for, the curve in the sanitary tee prevents solid waste traveling down the vertical stack from nicking and backing up into in the horizontal drain, where it can dry and clog. An equal/vent tee cannot prevent this. For the same reason, sweeps are needed for vertical to horizontal transitions, because otherwise the poopy poopy could land uphill and wouldn't get carried away.
    – Steven
    Commented Nov 30, 2023 at 8:26

2 Answers 2


A sanitary tee has a subtle curve down, I suppose in hopes of keeping your waste going in the right direction.

sani-tee image from Home Depot, not an endorsement

  • 6
    It's that, and it's more of an 89° than a 90° corner for the same reason.
    – Ecnerwal
    Commented Nov 26, 2023 at 23:25
  • @Ecnerwal In Chile, they're marked "87.5°". I guess code might call for a 5% slope? Not that the tolerances are within half a degree, anyhow...
    – Conrado
    Commented Nov 28, 2023 at 12:02

A sanitary tee has a curved center section to allow smoother, more efficient liquid flow. In drainage systems, it is primarily used to connect horizontal drains to vertical drains. The center connection is usually to the pipe leading to a trap. Sanitary tees should not be used to connect a vertical drain to a horizontal drain because of the likelihood that solids will build up at the bottom of the junction and cause a blockage.

Three Different Uses of Sanitary Tees

  • Sanitary tees can be used to join a horizontal line. For example, to join waste arms to vent stacks or vertical risers.
  • In some cases, a sanitary tee can also be used in place of a vent tee when plumbing vent lines. It helps to maintain the proper flow.
  • When installing sanitary tees, do not place them with the backside up and the side open because this will cause waste to splash upstream when it hits the bottom of the horizontal pipe. This will eventually cause blockages in the pipeline.


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