25/07/2025
The image shows examples of correct and incorrect ways to install plumbing fittings—like tees, wyes, 1/8 bends, and combo wyes—in horizontal drain lines, especially in relation to venting and the flow of wastewater.
Top Left – Incorrect Installation:
Fitting Used: A wye fitting with a 1/8 bend (also called a combo wye) connects a horizontal drain to a vertical stack, with a vent pipe attached to the side.
Problem: This setup is labeled "Restricts vent air" because the sharp bend can cause wastewater to splash or stick to the fitting, blocking the vent pipe. If vent airflow is blocked, it can create negative pressure in the system, pulling water out of traps and letting sewer gases into the building.
Indicator: A red đźš« symbol marks this as wrong.
Top Right – Correct Installation:
Fitting Used: A sanitary tee connects the horizontal drain to the vertical stack, with the vent pipe attached to the top outlet of the tee.
Why It Works: The sanitary tee is shaped to guide wastewater down smoothly while letting air enter the vent system from the top. This keeps the drain system balanced and prevents siphoning of traps.
Indicator: A green âś… shows this is correct.
Bottom Left – Incorrect Installation:
Fitting Used: A sanitary tee is placed horizontally where multiple fixtures connect.
Problem: The note "Waste backflows upstream" means that this tee, when laid flat, can block smooth flow between fixtures. Instead of allowing waste to pass through, it may cause backup into another fixture.
Indicator: Marked with a đźš« to show it's wrong.
Bottom Right – Correct Installation:
Fitting Used: A wye fitting with a 1/8 bend (or combo wye) is used to connect multiple fixtures in a horizontal line.
Why It Works: The angled design of the wye allows wastewater from each fixture to merge more smoothly, reducing the risk of blockages or backups.
Indicator: A green âś… marks this as correct.
Final Takeaway:
This diagram stresses the importance of choosing the right fittings in horizontal drain lines.
Use sanitary tees for vertical stack connections to ensure proper venting.
Use wyes (with or without 1/8 bends) for connecting horizontal drains from multiple sources to support smooth waste flow.
©️Lawyer RT