For years I kept adding filters and drain traps, but kept spitting water droplets after spraying for a while. Finally figured out that when the compressor is working hard, the moisture is in vapor form and will never get trapped in any filter or drain, but when the pressure is suddenly released at the spray nozzle the air is cooled and water droplets form..........same principal as your refrigerator works on. The best long term solution is a refrigerated air dryer if you want to spend $500 or more. There are desiccant systems available for less, that do the job, but require constant monitoring and changing the desiccant. Harbor Freight stuff is too cheap, but I find guns for $65 to $100 bucks work quite well. A good painter is constantly monitoring flow, fan and pressure. In fact when approaching an area where excess paint may cause a run, I simply lower the pressure that reduces the amount of product I'm applying without the need to adjust flow or fan. Good lighting is a must as is a very clean spray area.............one bug will ruin all the prep work!
Cheers,
JJ