Ok I get what your saying, but that makes no sense at all? If you open the valve on the top, how does the water get pushed uphill? If you want RO/DI you have to clear the line from the valve at the bottom, to the valve at the top. Just opening the valve on the salt bin will not clear the line. You have to push it uphill(back into the bin), and opening the valve on the bottom will just push more water into the line(pressure). With 1" piping, your probably mixing a gallon or 2 every time you want salt or RO/DI.To clear the line all you do is open the salt valve at top..let the salt line clear into the salt bin, shut off the salt valve at top, and then you have fresh RODI water throughtout the line.
I'm not calling you out, just trying to understand your thinking here and how it works. I considered doing it your way, but could not figure out how to not mix the 2 without a separate valve for just RO/DI.