When I was renting I used the faucet adapter with no issues. I kept the RODI system (RO Buddy) and all the hoses in a five gallon, kept them in the five gallon while it was running (to keep it vertical) ran the waste back into the sink. I was only running a single 15 gallon. I had three buckets, one to keep the RO system in, one to produce RODI water into, and one to mix salt. They all stacked and the first bit of RO that came out I used to give the buckets a quick dusting and rinse.
Had the RO make 4 gallons into the RODI bucket Friday night pour two gallons into the salt bucket. mix up my salt, do a water change, Pour some RO into my top off bucket (a three gallon bucket under my tank) kept the remain RO in a gallon jug for use throughout the week.
Now that I think of it, it was actually a really small amount of space I used... compared to the sq footage my RO system takes up now :grinning-face-with-sweat: