Several of my cats will also get feline acne from time to time and I use stainless steel bowls for drinking and eating. I've found that using a warm wash cloth will help to loosen up and get rid of the black flecks. Then I use some hydrogen peroxide to help keep it clean. It seems to work well but you need to keep this up for at least 1-2 times a day for a while. I've also noticed that stress will make them break out sometimes too. Good luck.