As i understand , you can define an inlet flow for pumps location and you will see water behaviour along the lon pipeways.
Maybe this video gives you a hint
However you are working on a mixing study, so you have to create more mesh.Maybe 10 cell for section.
This causes more calculation time
You can model this in Flow, but it's not the best application. Flow Simulation is for studying specific motion of fluids in and around intricate or novel geometry. Straight pipes, tees, and elbow bends are not novel or intricate.
Piping systems are a thoroughly studied subject, and there are many empirical relations for calculating pressure losses through piping sections, bends, and other features. By trying to model the flow in CFD, especially with software which you've never used before (I'm assuming), you're adding weeks worth of work to your project for no good reason.
If you insist on computational methods, there exists better tools for modeling piping networks. Look up 1-D flow network modelling.