I split mine off my washer hookup in the laundry closet.. Used a garden hose y adapter, washer on one side, rodi on the other, my waste goes down the drain to be reprocessed so I don't feel like I am "wasting it" other than paying for it, but water is still cheap here. I have a ball valve in the water supply line to the rodi unit to turn it on/off, so no connecting/disconnecting all the time.
Temperature plays a role in the rodi unit processing the water, so that is something to take into account if you are planning a garage install. What is your garage temp high and low?
Convenience in transporting water around is something to consider, how will you get water from rodi unit to the tank? Is there any impediment to rolling a brute trashcan around? my last garage had a 2in lip to get into the house, no way to roll something in..
My laundry closet is ten feet from the tank and has been a convenient spot, think about how you are going to use it not just where it's out of the way.