The Co2 discharger is for unloading your muzzleloader without having to fire your gun and dirty the barrel at the end of the day. I don't think most people who use one soak the breach in water before using it.
I have not used one, but I heard it is very effective, and it makes a distinctive "bloop" when it spits the dry charge and ball out of the barrel. As in 100% of the time, I would make sure the barrel is pointed in a safe direction (preferably a backstop) when using it.

C. Davis