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What is the minimum requirement for the slope of horizontal drainage pipes between manholes?

  1. 4%

  2. 2-1/2%

  3. 2%

  4. 3%

The correct answer is: 2%

The minimum requirement for the slope of horizontal drainage pipes between manholes is 2%. This slope is essential to ensure proper drainage and prevent the accumulation of waste water within the pipe. A slope of 2% allows for effective flow by using gravity to facilitate the movement of wastewater through the pipes at a sufficient velocity. If the slope is too shallow, there is a risk of sediment buildup and blockages, which can lead to system failures and backups. This standard is grounded in plumbing codes and practices to maintain the functionality and safety of the sewage system. The other options suggest slopes that are either too steep or not optimal for efficient drainage, potentially leading to increased wear on the drainage system and unnecessary energy expenditure to maintain flow, which is why they do not meet the minimum requirement.