Search on float switch, I think its Coralife that made one, you install it in the sump at the level you want to maintain, and hook up a connection to a collected water source from RO with a small power head, or, directly to RO. In my experience I ran the line from a laundry room sink into the basement below and up to the sump. I learned the hard way you need to turn down the water pressure on the RO on float switch. Just like it sounds like, turn the faucet pressure down. The laundry room sink had a cheap faucet so I replaced it with a kitchen or bathroom one which could be use a simple adaptor to connect to RO. You lose access to the sink basically.
On a collected water source you can also do calcium and carbonate hardness buffer, I put a little salt mix in the water, you need a second power head in the collected water to circulate it.
On a six foot tank, I managed to find two large oak corner cabinets I put to the left and right. One had a HDTV, one had a 50 gallon rubber maid with the lid on. Home Depot sold wheels for them so in one application I would fill RO in the garage and wheel it in. Yes, it’s heavy.
Not trying to be rude, but turning down water pressure does nothing but make the RO/DI inefficient. The RO/DI needs a certain water pressure to preform at it's peak. Also it's never a good idea to plumb straight from the RO as I mentioned earlier. Floats are prone to stick and reduced water pressure still does nothing for overflowing/filling the system with freshwater!!!!
