When I clean my breech plugs with the very smallnarrow fire channel, the way I find easiest to cleanthemis in the kitchen sink. Make up a solution of very warm dish water. Then with atooth brush, scrub the threads and the outside nice and clean. I then pump the plug up and down in the water like you can do with a glass to force water to climb up through it. When the outside is clean and I suspect the inside clean, I take it outside and spray the inside channel with brake cleaner. After that I go to the air compressor in the shop or my small can of air and spray the hole open and dry. After that I can re-grease it and am pretty certain it is nice and clean.

On the ones like the Black Diamond XR or Knight Wolverine which have a larger hole because of a nipple removal, I clean the pretty much the same way but then force Q-tips though the opening and center to clean all that out and to make sure it is dry.