I use boiling hot water and no soap, I treat it like a cast iron pan and never use soap, the "seasoning" in the barrel seems to last longer and the loading a bit easier, also I only use products that are made by TC because in most cases they are natural products and work just as well when used properly as the chemicals.
Also I run several bore butter impregnated patches through the bore while it is still hot since as in the case of the cast iron pan and oil it makes the bore butter fill the pores of the bore while they are open. I also put a small amount of anti seize on any threads (Breech Plug, Nipple, Bolt plug, etc...) and leave them just a touch loose !!
Make sure your ML is cooled then get a small cup of rice and place it in your safe or gun cabinet and store you ML in there, the rice will keep the moisture to a minimum and inhibit any rust !!!

Just run some clean dry patches through the bore and tighten up the plugs and nipple and load up ready to go !!!