What type of fitting should be avoided in a drainage system for efficient flow?

In a drainage system, cross fittings should be avoided for efficient flow because they create multiple flow paths that can lead to turbulence and increased resistance in the system. When wastewater flows through a drainage system, maintaining a smooth and continuous flow is crucial for effective drainage and to prevent blockages.

Cross fittings can cause the flow to split, leading to uneven distributions and potentially increasing the risk of clogging. In contrast, wye fittings are designed to direct flow smoothly and are typically used to connect two pipes at an angle, allowing for better flow dynamics. Sanitary fittings are specifically shaped to facilitate smooth transitions and reduce turbulence, helping to maintain proper flow in sewer applications. Adapter fittings serve more of a purpose in connecting different pipe sizes or types rather than affecting flow dynamics in drainage systems.

Thus, using cross fittings in drainage systems can hinder efficiency and should be minimized or avoided, supporting the choice of this option as the correct answer.