The image displays examples of proper and improper placements of plumbing fittings (tees, wyes, 1/8 bends, and combos) in horizontal drain lines, specifically concerning venting and waste flow.
Top Left – Incorrect:
- Fitting: A wye fitting combined with a 1/8 bend (or combo wye) is used to connect a horizontal drain line to a vertical stack, with a vent pipe connected to the branch of the wye.
- Issue: The diagram indicates that this configuration “Restricts vent air“. The sharp angle created by the wye and bend can cause wastewater to splash or cling to the side of the fitting, potentially blocking or reducing the airflow in the vent pipe. A blocked or restricted vent can lead to negative pressure in the drain system, siphoning water from traps and allowing sewer gases to enter the building.
- Marking: A red circle with a diagonal line (🚫) signifies this as an incorrect installation.
Top Right – Correct:
- Fitting: A sanitary tee is used to connect a horizontal drain line to a vertical stack, with the vent pipe connected to the upward-facing branch of the tee.
- Function: The design of a sanitary tee allows wastewater to flow smoothly downwards into the vertical stack while providing a clear path for air to enter the vent system above the drain line. This ensures proper ventilation and prevents trap siphonage.
- Marking: A green checkmark (✅) signifies this as a correct installation.
Bottom Left – Incorrect:
- Fitting: A sanitary tee is shown installed in a horizontal drain line where multiple fixtures connect.
- Issue: The diagram illustrates “Waste backflows upstream“. In a horizontal orientation, a sanitary tee is designed to direct flow primarily downwards (or upwards for venting). When used horizontally for drainage, the internal baffle can impede the flow from one branch to the other, potentially causing wastewater to back up into the other connected fixture.
- Marking: A red circle with a diagonal line (🚫) signifies this as an incorrect installation.
Bottom Right – Correct:
- Fitting: A wye fitting combined with a 1/8 bend (or combo wye) is used in a horizontal drain line to connect multiple fixtures.
- Function: The angled branches of a wye fitting, when used horizontally, allow for a smoother confluence of wastewater flow from different fixtures, reducing the likelihood of backups or obstructions.
- Marking: A green checkmark (✅) signifies this as a correct installation.
In summary, the image emphasizes the importance of using the correct type of fitting in horizontal drain lines to ensure proper wastewater flow and adequate venting. Sanitary tees are appropriate for connecting horizontal drains to vertical stacks for venting, while wye fittings (often with 1/8 bends) are better suited for joining multiple horizontal drain lines.
