No real solution needed. As was posted, room temperature (NOT hot) does a great job. Bob Hill recommended simple blue windshield washer fluid (WWF), and it does work better. Not earthshaking, but maybe 10% or 20% better, but better.
I plug my touch hole or nipple and fill the bore with WWF, let it sit five minutes, them pour it out. I repeat that process, then use the WWF on patches to clean the bore. Sometimes few patches until clean, sometimes a lot of patches. I dry the bore, and clean the bore again with Mr Flintlock or Lehigh Valley Lube (LVL, same formula for both) that takes out graphite. I again dry it, and wet the bore good with WD 40 to remove moisture remnants. I take the gun home, and the next day dry patch out the WD 40. I then scrub it good with wet patches of Break Free Gun Oil and it's done.
May sound lengthy, but my bores aren't rusted, and I live where it is humid. BTW, if you store vertically, it is safer to store muzzle down so no oil creeps into the wood at the breech.
God Bless, Marc