yeah i have it hooked up from my hose going into the filter process then after my resin. the guy i bought my ro/di unit from had it hooked up to flush the membrane and never switched it back apparently
Once the water is coming out the correct output it should be slow.. like 2 gallons per hour roughly. This water should be your zero TDS water... Wishing you luck.
You can disregard the level controller but pay particular attention to the "End View For Membrane" box for the correct positions of the waste and treated lines.
The diagrams are generic and could apply to any RO or RO/DI system.
Make sure you have the flow restrictor in the waste line and your waste to treated ratio is close to 4:1. What you are calling a check valve may be the flow restrictor, does it have something like 500m/L stamped or printed on it anywhere?
A photo or two would really help troubleshoot the system but it should be pretty easy to figure out.