I'm no expert, but when I had a caplock, the way I cleaned it was to remove the barrel from the stock and stick the breech end into a pail of HOT soapy water. Scrub around the nipple area with an old toothbrush. I then ran a patch down on a cleaning jag and "pumped" the water up and down the barrel through the nipple. It cleaned the black powder out in no time.
Then, I took the barrel out of the pail, and poured REALLY HOT water into the muzzle, holding the barrel with a heavy rubber glove. The water will run out the nipple and the barrel will get real hot.
When the water's all out, I run a couple of clean patches down to get any water out near the breechplug, and give it a couple of minutes for any remaining vapor to evaporate. Then run whatever rust preventative/oil you like to use down on a patch. It also is a good idea to remove the nipple and clean inside it real well with pipe cleaners - as well as the passage that goes from nipple to breech.
Obviously, you also clean carefully around the lock andtrigger before coating with your favorite oil for storage.

IM jaybe