Wye Fitting

A wye fitting (also written "Y fitting") is a drain-waste-vent (DWV) fitting shaped like the letter Y, with a branch that meets the main pipe at a 45-degree angle rather than 90 degrees. The angled entry creates far less turbulence than a 90-degree tee connection, making the wye the preferred fitting for horizontal drain connections and for connecting horizontal branch drains to horizontal mains.

Wye fitting or sanitary tee — what's the difference?

Both fittings branch a drain line, but they serve different configurations:

• Sanitary tee: 90-degree branch with an internal sweep — correct for vertical stack connections; forbidden for horizontal-to-horizontal connections
• Wye: 45-degree branch — required (per IPC) for horizontal branch-to-horizontal main connections and for any horizontal-to-vertical transitions when combined with an eighth-bend (1/8 bend or 45-degree elbow)

What is a combo fitting?

A combo fitting (combination wye + 1/8 bend) combines the wye with an attached 45-degree elbow at the branch entry in a single factory fitting. This is the standard fitting for connecting a horizontal branch drain to another horizontal drain, reducing the need to assemble separate fittings in tight spaces.

What code requirements apply to wye fittings?

The IPC and UPC require that all horizontal DWV connections use fittings that "change direction" of flow smoothly — no fittings that create a reversal of flow direction. A wye or combo fitting meets this requirement for horizontal connections; a sanitary tee on its side does not (it would direct flow upward into the branch).

How are wye fittings installed?

PVC and ABS wye fittings are solvent-welded (glued) using appropriate primer and cement. Cast iron wye fittings use either hub-and-spigot joints with lead and oakum (old) or neoprene gaskets and hubless Fernco couplings (modern).