Do you know how to make a homemade black powder solvent (this is a question for hunters)?

I need to know how to make a black powder solvent/cleaner that really really works to clean a traditional black powder rifle that doesn't like to fire beacause of the breach plug not getting thoroughly cleaned( this Gun Is Not An Inline so you can't take the breach plug out)Do you know how to make a homemade black powder solvent (this is a question for hunters)?
I've always just used lots of hot soapy water (dawn dishwashing liquid). Of course, you have to get it really dry afterwards. I also drilled out my nipple to 1/16th inch. and I always use a pipe cleaner to clean out the tunnel from the nipple to the inside firing chamber. I'm not sure what you would need to do if you had a flintlock. I've never had one of those. Mine is a T/C .50 cal Hawkins. I've never had a misfire with it.