What is the maximum distance between manholes on underground drainage lines with a diameter of 10 inches or larger?

• A. 100 ft
• B. 125 ft
• C. 200 ft
• D. 150 ft

Answer: (D)

Maximum spacing between manholes is set to ensure regular access for cleaning, inspection, and maintenance of gravity underground drainage lines. For lines with a diameter of 10 inches or larger, the standard maximum distance is 150 feet. This spacing keeps blocks or debris from going too far without access, making it feasible to use rodding or other cleaning methods and to inspect the line without removing long sections of pipe. If the distance were greater, accessing and cleaning a blockage becomes more difficult and the risk of undetected issues increases. Smaller or differently sized lines may have different spacing, but 150 feet is the typical limit for 10-inch-or-larger sewers.