Here are some pics on how I have mine setup.
This pic is my fresh RO/DI water on left and salt mix water on right.
Here it is using the john guest fitting into the pvc plumbing
After a bit of experience I've figured out you can thread john guest fittings into PVC with no modifications to either pvc or john guest fitting.
and a pic of the same unit you're looking to purchase.
Hope that explains a little more.