Here's a few pictures that show how the plumbing works. In the first one saltwater from the tank on the right is pumped to the top horizontal line to the tank. In this picture water is pumped from the right hand tank and straight up to the vertical valve that will lead back through the top of the same tank. This will circulate water to mix the saltwater in this tank. In this picture RO/DI water from the left tank goes to the bottom horizontal valve that will lead to my ATO reservoir. And in this picture water will go from the left hand tank to the right hand tank to prepare for mixing. Play like the second valve from the right is closed because it would be.