How should manholes be spaced?

• A. 600 feet for all sizes
• B. No further than 400 feet for pipes 15 inches or less, 500 feet apart for 18 inches to 30 inches
• C. 200 feet for all sizes
• D. 1000 feet for all sizes

Answer: (B)

Access to the sewer line for cleaning, inspection, and maintenance drives manhole spacing. Smaller pipes need more frequent access because they are more prone to blockages and are cleaned with shorter, more precise equipment runs. Therefore, the maximum distance between manholes is set tighter for pipes 15 inches or smaller—no more than 400 feet apart. For larger pipes, specifically those 18 inches to 30 inches in diameter, you can space manholes a bit farther apart—up to 500 feet. This arrangement provides practical access for maintenance while avoiding unnecessary extra manholes on bigger-diameter lines. Spacing choices like 600 feet for all sizes or 1000 feet would leave small-diameter lines hard to clean and inspect, while 200 feet for all sizes would be excessive for larger pipes.