Glossary
Wye Fitting
Also known as Y-fitting
A fitting with three ports arranged in a Y shape, used to branch one pipe into two or combine two lines into one.
A wye fitting has one inlet and two outlets (or vice versa) positioned at roughly 45 degrees to the center line, not 90 degrees like a tee. This angle reduces turbulence and pressure drop, making it the go-to for waste and vent lines where smooth flow matters. In drain-waste-vent work, wyes are preferred over tees because the gradual branch helps solids move through cleanly without hanging up.
You'll run into wyes most often where a secondary drain merges into a main line—toilet and sink drains combining into a single stack, for example. They come in PVC, ABS, and cast iron, and sizing follows standard nominal pipe diameters. Code generally favors wyes over tees in DWV applications because they perform better under load and reduce the risk of blockages at junctions.
When you're laying out a vent line or a secondary drain, reach for a wye instead of a tee. The angle pays for itself in fewer callbacks for slow drains and backed-up secondaries. Sanitary wyes (with a long-turn inlet) are the refined version for critical junctions and are worth the extra cost on jobs where performance matters.