you shouldn't need to flash your water based colors, unless you are trying to put a second coat for more opacity. we do up to 8 color wet on wet water based printing all the time, no flash unit at all. If you are trying to do an additional coat for higher opacity, you need to either flash longer, for water based ink, you are going to really need more time flashing than plastisol to evaporate the water out of the image, which can be tough on lighter shirts as the longer you flash, the closer to scorching you come. If your colors aren't opaque enough, you need to deepen the pigment load by a couple maybe 4-5% more. Or use a lower mesh count to get more ink into the shirt fabric in one pass. Depending on what type of flash you have, and how much heat it puts out, you could be there all day trying to flash water based prints and the flash is not even necessary as the inks are designed for wet on wet printing.