How to simulate a wastewater effluent diffuser in SewerCAD

SewerCAD is not the best choice for this analysis since you would need to specify the slow split at each diversion in the GVF solver.

Since the pipe will be flowing full, WaterCAD is a much better choice and you can model each opening as the equivalent area round pipe or with the appropriate emitter coefficient.

In general, you'll find that you get the most even distribution of flow between outlets when the outlet size is small with regard to the pipeline size. You'll get the most flow out of the most upstream outlet since it has the highest pressure (assume a flat bottom).