In sewer piping, the invert refers to which part?

• A. Bottom
• B. Top
• C. Water line
• D. Center

Answer: (A)

The concept being tested is what the term invert means inside a sewer pipe. The invert is the bottom interior surface of the pipe—the lowest point inside where wastewater actually flows. This bottom reference point is used to determine the invert elevation, which sets the slope or grade between pipe joints so gravity can carry the wastewater forward. It’s also the point where pipes connect to a manhole, guiding how the flow enters from one segment to the next. Because flow depends on the vertical difference between inverts, engineers use the invert to calculate fall and ensure proper drainage. It’s not the top interior surface, not the centerline, and not a waterline.