Lycoming (RSA) injection systems can be (and are) pressurized by the fuel over a variable range with the main and boost pumps and simply "take what they need" based on the mass flow of air going through the intake. 

Continentals work on a carefully balanced fuel pressure and "throttle position with an orifice" scheme that requires any unmetered fuel to get dumped back to the tank.

For the RSA, simply run the line from the main pump to the servo and then from the servo to the flow divider. The "Gage" outlet on the flow divider is flow divider pressure and becomes a rudimentary flow meter when connected to a "flow" gage in the cockpit. That gage must be calibrated to the system's particular pressure vs flow curve, that is, you need to buy the right gage to get the right fuel flow reading. They're not that accurate anyway, and more of a final fuel pressure gage. I'm also using a modern Electronics International flow meter and fuel totalizer right in front of the flow divider for accurate fuel measurement.

There is also a line coming off the flow divider that is an atmospheric vent which allows the diaphragm to open and close and serves as a fuel drain in the event the diaphragm springs a leak. That line should be run overboard like the main fuel pump and boost pump vents, but don't angle the line into the airstream line a fuel tank vent. You don't want it getting pressurized which would try to close the diaphragm. Not good on your first takeoff! I'm using a Viton hose from McMaster-Carr for that line.