Correct me if I'm wrong but I don't think you guys want to restrict your water flow before the head pipe. Pretty sure the idea of the flow control valve is to limit water buildup in the water box when at low RPM's tooling around. You don't want it pumping full force into the water box/stinger inlet when your not on the throttle, so this valve, until your water pressure reaches a certain point, will deflect water out a pisser instead of into the box.
You need to install it right before the stinger, with a T connector before the valve. Run the "straight" exit from the T to the flow valve, and the T'd part to your pisser. I think they recommend a 5mm restriction in the pisser to help build up pressure for your valve.
Thats what I gathered from this, just my .02 cents could be wrong. Maybe someone else will chime in with more knowledge.
Edit: Just read those instructions, I was definitely right. Designed for water box water restriction.