I want to setup a bit of a conceptual simple but painfully difficult to find part system where i have two pipes one with ro water and one with filtered water and i want several set of valves that can mix ro and filter water to get a target tds; my difficulty is finding the right kind of mixing valve that can mix the two types of water in some measure quantity or %. It seems like such a thing should exist and in my searching i now and then see reference to a mythical TDS bledning valve but never an actual stand-alone product.