The passage between compartments of a septic tank shall be located what percentage below the liquid level?

The correct response identifies that the passage between compartments of a septic tank should be located 25% to 50% below the liquid level. This positioning is crucial for effective septic system functionality.

By placing the passage at this level, it helps to optimize the flow of wastewater between the compartments while maintaining the proper treatment process for solids and effluent in the tank. It ensures that the bulk of the settled solids remain in the primary compartment, thus allowing for adequate separation and microbial action to occur. Optimal placement within this range also minimizes the risk of scum or foam escaping into the second compartment, which could disrupt the treatment process and lead to issues with the overall efficiency and longevity of the septic system.

The design parameters are based on the need to balance hydraulic flow and treatment capacity, making the 25%-50% positioning ideal for keeping the processes effective while minimizing solids transfer between compartments.