I do the same as most here, plug the vent, luke warm water to to muzzle for 5 minutes, pour it out. Do it again 2 times. Then bring it inside for patches.
But this rifle takes dozens and dozens of patches, before they start coming out clean. I think the cause is I don't have a brush that fits my rods, and the bore. So I'm slowly wiping the residue out of the deep, round bottom grooves each pass. I need to add a brush to the first few steps and I'm sure it will clean with 4-5 patches. I hope.
In the past I didn't need a brush, because I had percussions. I would put a special nipple with a rubber hose in a bucket, and a tight patch on a rod, pumping water back and forth a few times. I could have clean patches in 5 min. Flintlock? Not so much.