how to use a moisture trap

i've got one integrated into the pressure regulator but it doesn't seem to be cutting it, probably because i don't know how to use it. what i do is try to open the spigget at the bottom regularly to let whatever moisture out. problem is, there doesn't seem to be much of anything accumulating and after probably half an hour of airbrushing (yeh, i get carried away...) water starts sputtering out of the airbrush anyway. the hose is only 6 feet long from the compressor/trap to the brush. i'm considering getting a small in-line trap to put right before the airbrush but i figured i'd ask if i'm doing something obviously wrong first. any advice? thanks in advance.