The distance interval for installing a relief vent along the main drainage line is ______.

The distance interval for installing a relief vent along the main drainage line is ______.

• A. 100 feet
• B. 200 feet
• C. 300 feet
• D. 400 feet

Answer: (B)

Relief vents on the main drainage line are spaced to keep air from being blocked in the pipe as water and waste move through, preventing negative pressure that can siphon traps. Placing a relief vent about every 200 feet provides a reliable air entry point along the run, helping traps stay sealed and reducing the chance of sewer gases entering the building. This interval strikes a practical balance between effective venting and not overdoing the number of vents. If the distance were much longer, a strong vacuum could develop; if it were shorter, you’d add vents unnecessarily.

Relief vents on the main drainage line are spaced to keep air from being blocked in the pipe as water and waste move through, preventing negative pressure that can siphon traps. Placing a relief vent about every 200 feet provides a reliable air entry point along the run, helping traps stay sealed and reducing the chance of sewer gases entering the building. This interval strikes a practical balance between effective venting and not overdoing the number of vents. If the distance were much longer, a strong vacuum could develop; if it were shorter, you’d add vents unnecessarily.