I can draw up a diagram of you wish but it's pretty straightforward. Essentially you build your manifold with however many outlets you feel you may need, in my case I had 4. 2 for reactors, one spare and one for water changes. These are fed by a pump of your choosing. Just think of it like building a manifold into your return line, but the end of the manifold just stops and doesn't continue into the tank. GPH will greatly depend on what you would like to run off the manifold, your pump has to provide the right amount of flow for all the outlets in use. DC pumps are great for this as you can ramp up the flow when you have a lot of the outlets in use or tone it back when you don't. I used an AC pump (Mag 7) on mine as it was mostly just for carbon and WC's so a specific flow wasn't really required and I used gate valves to fine tune the flow when needed.
Just a basic drawing to give you an idea...