Well after a few teething problems with my backpack, with varied tds figures between 2 - 6 ppm. Results were a little disappointing. I was beginning to think WFP just wasn't the viable method it is heralded to be. So I stuck with it, ordered another 4.6 ltr DI, to double up my tanks. Then reduced the flow a bit on the pump, as well as installing a trigger so I am not wasting so much water and time. I redid my own windows, as well as trad'ing all my inside windows to see what the results were like. Perfect. No runs no spotting, nothing. My TDS is now a steady 000. I now have two questions I would like to ask all the WFP pro's. What TDS do you change your resin at? Secondly my trigger value, which I go from fullCleanCentre http://www.fullcleancentre.com/mini-ball-valve-short-handle-1-4-ff/ has a little leak, can I just wrap that in plumbers tape, it seems to be fairly well srewed on, but still dribbling water.