Sanitary Tee

A sanitary tee is a drain-waste-vent (DWV) fitting with a T-shape where the branch inlet has a curved (swept) entry that directs flow in one direction only — downward into the main drain. The curve (sweep) prevents solids from hanging up in the fitting and ensures wastewater flows smoothly from the branch line into the vertical stack. Sanitary tees are one of the most common DWV fittings in residential plumbing.

How sanitary tees differ from standard tees

A standard (plumbing) tee has a straight-through pattern with a 90-degree branch opening. This is fine for venting (where only air flows) but not for drains — the sharp 90-degree turn creates turbulence, slow flow, and clogs. A sanitary tee's swept branch has a gentle curve that transitions flow direction smoothly. The asymmetry means sanitary tees are directional — they install with the sweep pointing downward toward the direction of drain flow.

Code usage restrictions

The International Plumbing Code specifies exactly where sanitary tees can and cannot be used:

• Allowed: branch drains connecting into vertical stacks (the curved branch faces the direction of vertical flow)
• Not allowed: horizontal-to-horizontal connections — a sanitary tee used on its side would direct flow up into the branch rather than down. Use a wye + 1/8 bend combination or a combo fitting instead.

Typical applications

• Connecting lavatory, bathtub, or laundry drains to a vertical soil stack
• Stack connections in multi-story DWV systems
• Vent connections at the top of stacks

Material

Sanitary tees are available in PVC (Schedule 40), ABS, cast iron (hub and hubless), and copper. PVC and ABS are standard for new construction; cast iron is used where noise reduction is a priority (apartments, hotels).