What device is designed to prevent backflow from the sewer into a building?

• A. Cleanout Cap
• B. Sump Pump
• C. Grinder
• D. Backflow Preventer

Answer: (D)

When sewer backups threaten a building, the device you want is one that blocks flow coming back into the structure. A backflow preventer sits in the main sewer line and acts as a one-way gate: it allows wastewater to flow out to the sewer, but closes off if the sewer line pressure pushes backward, preventing dirty water from entering basements and fixtures. The other devices don’t serve this purpose: a cleanout cap is just access for cleaning; a sump pump moves groundwater away and doesn’t stop sewer backflow; a grinder breaks up solids but doesn’t block reverse flow. So the device designed to prevent backflow into a building is the backflow preventer.