What should be placed in the discharge pipe to prevent siphoning when field lines are below the operating water level?

To prevent siphoning in a septic system, particularly when field lines are situated below the operating water level, a vacuum breaking device is implemented in the discharge pipe. This device is specifically designed to break any potential vacuum that could form within the system, which is essential for maintaining proper flow and preventing backflow.

When pipes are laid out in a configuration where gravitational forces could create a siphon effect, the risk of wastewater being drawn back into the system could lead to contamination or system failure. The vacuum breaking device introduces air into the system when a vacuum is detected, effectively neutralizing the siphoning action and ensuring that the wastewater flows in the intended direction.

While float switches, air vent valves, and check valves have their respective roles in septic systems—such as controlling liquid levels, allowing air movement, and preventing backflow—they do not specifically address the siphoning issue linked to lower field line installation. Thus, the vacuum breaking device is the most appropriate solution in this scenario, ensuring safe and efficient operation of the septic system.