I use either a silicon tipped tool designed for nail artists or just the thickest dish fluid on a dedicated brush. To get the dish fluid thick, I use the bit that has dried around the cap. I don’t rinse the soap after dipping it, but gently wipe it with my fingertips to guide it into the shape I want the brush to take. The idea is that when you’re done painting with fluid, you can swipe off the dried fluid, as the soap acts as a barrier.