If a drain is subject to back flow, it shall be equipped with a _______ _______?

• A. Backwater Valve
• B. Check valve
• C. Air gap
• D. Siphon breaker

Answer: (D)

Backflow protection for drains relies on a device that acts as a one-way barrier in the building’s sewer line. The appropriate fitting to prevent sewage from backing up into the structure is a backwater valve. It lets wastewater flow out to the sewer but automatically closes if the municipal sewer pressure rises, blocking the reverse flow. A check valve can provide similar protection in some piping, but for drainage systems the backwater valve is the standard solution. An air gap serves to protect drinking water supplies by creating a physical separation, not to stop sewer backflow. A siphon breaker (anti-siphon device) prevents traps from being siphoned dry due to negative pressure, not backflow into the building.