For sanitary building sewers 6 inches or smaller, what is the maximum distance between manholes?

• A. 200 feet
• B. 400 feet
• C. 600 feet
• D. 800 feet

Answer: (B)

Access for cleaning and inspection drives how far apart manholes can be placed. When sanitary building sewers are six inches in diameter or smaller, the system needs more frequent access points so crews can locate and clear blockages with standard rodding equipment and still maintain control over flow and venting along the line. Because of this, the maximum distance between manholes is set at four hundred feet.

If the spacing were much shorter, you’d add unnecessary cost and more access points. If it were much longer, locating and clearing a blockage would become difficult and the system could lose effective maintenance access. Larger-diameter pipes can tolerate longer gaps between manholes, but for six inches or smaller, four hundred feet is the established limit.