Which feature must be included to connect adjacent trenches in a serial distribution system?

In a serial distribution system for septic installations, tight joint 45-degree elbows or tees are essential for connecting adjacent trenches. This is due to the need to maintain a smooth flow of effluent between the trenches. The tight joints ensure that there are minimal leakage points which can compromise system efficiency and potentially lead to environmental hazards.

Using 45-degree angles helps facilitate the flow direction without causing turbulence that might occur with sharper angles. This design is particularly crucial in maintaining effective gravity-fed systems, as it allows for a gradual change in flow direction, thus avoiding blockages and ensuring that effluent moves efficiently through the system.

Other options, such as flexible tubing, adjustable connectors, and standard PVC couplings, may not provide the same level of reliability and performance in a septic system context. Flexible tubing might not ensure a secure connection, adjustable connectors can lead to issues with alignment, and standard couplings may not offer the necessary angle for connecting trenches effectively. Therefore, the use of tight joint 45-degree elbows or tees is the optimal choice for achieving a reliable and efficient connection in this type of distribution system.