When you set out to plumb an aquarium set-up with a sump, the more planning / thought you put into the original set-up, the better it will be in the long run. This is not a very hard thing to do at all, if you focus on the basics and understand them. I tend to think of it in flowing different steps: A) Planning of your flow rates, B) planning the material types and sizes, and C) installation / set-up of the plumbing system. All of what you are about to read below is based on my experiences with various data from some North American manufactures of plumbing products (IPEX, Canplas, and Boshart) which is also detailed in the American Society for Testing and Materials (ASTM) standards.
I will explain what I mean by each step then I will show you examples from one of my reef tanks