What is the term used for the inside bottom elevation of a sewer line or drain pipe?

The term "Invert" refers specifically to the lowest internal point of a sewer line or drain pipe. This is crucial for drainage systems because the invert elevation determines how effectively wastewater will flow through the pipes by allowing gravity to assist in the movement of water. Invert elevations are key reference points for engineers when designing sewage systems, ensuring proper slope and slope calculations to maintain efficient drainage.

The other terms, while related to construction and surveying, refer to different concepts. A benchmark indicates a fixed reference point used in surveying to measure elevation changes, grade refers to the slope or incline of a surface, and elevation generally denotes the height of a point in relation to a base level but does not specifically indicate the lowest point inside a pipe. Hence, the use of "Invert" is appropriate as it precisely describes the inside bottom elevation of a sewer line or drain pipe.