Hearing protectors are recommended, for you also. We sell simple, inexpensive disposable ones in our arsenal store. Wait several minutes before reloading, making sure no live amber's are still in the barrel. Clean out the ash with a bottle brush or cleaning kit. Inspect the cannon, and insert another fuse, repeat steps above.
Black powder is very fouling and subsequently very corrosive.
A good solvent is simply a mixture of soap and water. Dry it, and then apply a light coat of oil. It really is important to clean and oil your cannon. With breech loading cartridge cannon, it is important to keep the firing mechanisms in good operating condition. Taking care of your cannon will insure that it will last a life time.