Howdy
Unless you have particularly stubborn fouling there is usually no need to soak the gun. Hot water is really the best solvent you are going to find for Black Powder fouling. The trick is being sure you remove all the water again when you are done, so you don't get rust. I usually just use a few patches soaked in my favorite water based BP solvent and run them through my chambers and bore at the end of the day. The fouling melts right off. A few Q-tips soaked in the same solvent will usually help in the nooks and crannies. A cartridge revolver is usually a bit simpler to clean that a C&B revolver because the chambers are bored straight through. A C&B cylinder usually has several nooks and crannies down in the chambers, and you can't push a patch staight through from one end to the other.
My favorite solvent also has oil dissolved in it, and when the water evaporates the oil is left behind. Here is the beautiful part: Black Powder fouling cannot cause rust if you soak it in oil. BP fouling is normally extremely dry, and in the dry state it wicks moisture in the form of water vapor out of the air. The water condenses and causes rust when it is held close against the metal by the fouling. But if you soak fouling in oil, it is 'full', and cannot absorb any water from the air. So it becomes harmless. When I am done cleaning my guns I run a patch soaked with straight Ballistol through the bores and chambers. Then I run a dry patch through to soak up the excess. In addition, I work a little bit of Ballistol down into the lockwork with a Q-Tip through the opening for the hand in the back of the frame. Any fouling that is lurking down inside the gun gets coated with the oil and is rendered harmless. I only tear my guns down once a year to completely degunk them. There is always some black, oily gunk down inside, there is never any rust.
Yes, conventional wisdom is that all oil should be removed from chambers and bores before firing a gun. To tell you the honest truth, I never do. I just load them and shoot them with that light coating of Ballistol that is down in the chambers and bore.