Short definition
A tee is a 90-degree branching fitting with three openings — two on the run (in-line ends) and one perpendicular branch. Available in every pipe material and joining method. The most common branching fitting in residential supply plumbing; in DWV, sanitary tees are used vertical-to-horizontal and wyes are used horizontal-to-horizontal.
What it is
The basic shape is unmistakable — a T-shape, with the run passing straight through and the branch teeing off at 90 degrees. Variants:
- Equal tee — all three openings the same size.
- Reducing tee — branch outlet a different size from the run.
- Sanitary tee — DWV-specific, with a curved sweep at the branch entry that directs waste downward. Used vertical-to-horizontal in DWV.
- Drop-ear tee — tee with mounting tabs (similar to a drop-ear elbow).
Why it matters to a homeowner
Tees come up in every multi-fixture plumbing job. Adding an icemaker, a basement bar sink, or a new bathroom requires teeing into existing lines. The supply-side rule is straightforward: a tee branches at 90 degrees with no specific orientation requirement. The DWV-side rule is stricter and worth knowing: a sanitary tee is for vertical-to-horizontal flow; a wye is for horizontal-to-horizontal. Get this wrong and the inspector will catch it.
Common variants and what a tee is not
- Tee vs. wye. Tee branches at 90 degrees; wye at 45. In DWV, code rules specify which is allowed where.
- Sanitary tee vs. straight tee. Sanitary tee has a shaped curve at the branch — vertical-to-horizontal DWV only.
- Reducing tee — branch outlet smaller than the run.
- Drop-ear tee — tee with mounting tabs.
Common failure modes
- Wrong tee in DWV (sanitary vs. straight) — code violation, drain flow issues.
- Tee installed backward in DWV — recurring clog point.
- Cracked plastic tee from impact in unconditioned spaces.