I usually set the nipple to soak while I'm cleaning the barrel. I've tried dish detergent, alcohol, peroxide, alcohol/peroxide/Murphy's and a bore cleaner I used to mix and use. None seemed to work any better than the other. When I'm done with the barrel I take the nipple and clean it under water in the hot water/detergent bucket I cleaned the barrel in. I use sections of pipe cleaner about an inch long and cleaning underwater pumps the solution back and forth through the flash hole. I never attempt to clean the flash hole with anything for fear of damaging it. I usually have to scrape some of the fouling around the flange to shoulder joint with a knife or pick. Do not use cheap pipe cleaners or craft ones, go to a tobacco store and buy the best. I have a cutter that will cut the wire without leaving a burr. Soaking for longer makes it slightly quicker to clean but honestly it takes about as long to clean a nipple as it does to read this so why bother? BTW, I clean my revolver nipples the same way however I never remove them. They are installed using anti-seize or choke tube lube and only removed to replace, never had any problems there.