I’ve been stuck on this problem for a while now. I have the Axeon 4040 membrane and housing. The problem I am having is that I go to five different houses a day, all with different water pressure and I don’t know how to ensure the pure water to waste water ratio is correct. Currently I just have a hose shutoff valve on the RO concentrate and I adjust till “it seems about right”. I know i’m doing damage and wasting water but I don’t really know what to buy to fix the problem. It seems like the answer should be really obvious, but I can’t figure it out myself. Any advice on the topic from other DIY RO users would be appreciated.