Which fitting is not recommended for changing direction in a drainage line?

The 90-degree elbow fitting is not recommended for changing direction in a drainage line because it creates a sharp turn that can lead to increased resistance and a higher likelihood of clogs. In drainage systems, a smoother transition is necessary to allow waste water to flow efficiently and to minimize the risk of build-up in the pipes.

Using fittings that create gentler changes in direction, such as 45-degree wye branches or long sweep elbows, promotes better flow and reduces turbulence. These types of fittings lessen the strain on the system and help maintain optimal drainage functionality. The combination wye and 1/8 bend also serves the purpose of changing direction while minimizing potential obstructions in the flow.

In summary, the 90-degree elbow fitting is less favorable in drainage applications due to its propensity to hinder optimum flow and potentially cause blockages, while alternatives like the other fittings mentioned support smoother and more efficient transitions in the plumbing system.