I found the best place for mine is the laundry room. It is mounted on the wall above the laundry sink so I can place buckets or jugs in the sink to fill. If I forget and they overflow its no big deal since it goes down the drain.
I used a garden hose wye adapter on the washing machines cold water line to feed the RO/DI and the waste drains into the sink. It could also be plumbed in to the faucet or cold water lines on the sink using adapters such as these but I chose the simple route:
PLUMBING ACCESSORIES FOR RO