Couple reasons for running ro to a large container and not directly to your sump.
first is safety, those float on/off switches have a pretty high failure rate. also, murphy's law says it will eventually fail when you least expect it and you don't want it failing to an infinite source of water. its a cheap safety check to have it fed by a pump that you can shut off in case salinty drops, etc.
second is the ro is most efficient running for long periods instead of on/off. the ro water that comes out when your first run the ro is usually higer tds than later on. you can check this with a tds meter.
hope that helps and great tank build.
My RODI is literally a floor below and on the opposite end of the house. I had the 1/4 inch tubing ran and drilled up to through the floor when the house was built. So what if I drip the RO water into an acrylic 10 gallon box with a float switch and then go from the acrylic box to the sump? Doesn't that just give me 2 pieces of equipment for possible failure now? It just seems like the float switch can fail just as easy in the container as the sump. I'm guess I'm not seeing what you are talking about here. Would love some more feedback and/or ideas.
Thanks