Most of the dirty water will come from the top frame - right over the top of the openers. Run your finger along it and see. Other areas are any vents and even the rubber seals. Just keep going and try to understand where the dirt comes from. It's all part of wfp. It doesn't work well 100% of the time and you need to refine your technique over time. I've been doing it for four years or more and can always find fault if i look hard enough.
