Update: I finally got this plumbed in without any leaks. What a fiasco! The shut off valve from the wall was corroded in the open position and the cheap white metal handle simply crushed to a jagged mess when I applied the pliers. Then, the threads of the chintzy plastic T stripped very quickly while trying to get it at the right (weird) angle between the valve and the hose to the sink. I tried some Flex Seal tape but that was a total fail. So, 2 soaking bath towels later, I got the hose back on what was left of the shut off and walked away. Of course with the quarantine, I couldn’t just run out for parts.
I bought/ordered a Shark Bite shut off valve and replaced that first. That worked great. Then I added a brass T and that fit too. Wonder of wonders! Finally, I added the reducer to go to the 1/4 inch plastic tubing to the RODI unit. Voila! Turned the water on and gave myself and the whole bathroom a good shower . I had forgotten the tiny, absolutely indispensable, hard plastic piece that keeps the plastic tubing from being crushed and leaking in the compression thingy.
Im so glad y’all are here. I just kept saying to myself, I’m gonna do this and I’m gonna post that it worked. And guess what! I finally made my first 2 gallons of RODI water! Thanks, all, for your support!!