Cleaning an inline isn't impossiable to do with hot soapy water. I should clarefy the water is really supposed to be
scalding hot.
You need a hose kit that hooks to the nipple or into the breach plug some way. with the proper sized jag on a ram rod (range rod) with a thick patch. useing a pumping action the barrel should come clean in just a half dozen pumps once the action has filled the barrel with the hot soapy water. Dump that dirty soapy water and refill the pail with scalding clean water to rince. A few strokes with a clean patch on the jag should be enough. The water being scalding hot should have heated the barrel enough it drys it's self. But a new clean oiled patch should be run down the bore never the less. If it is going to be long term storage use a oilier patch than for short term storage.
Useing this medhod for many a year in my Hawkins and Plains rifle. The Hawkins has a tang mounted peep sight, the Plains rifle has a T/C quick release removable scope mount.
On my Remington 700 ML's I just use rubbing alcohol. Remove the bolt and take it down. Place it in a bowl to soak, remove breach plug and nipple and place that in the bowl to soak in rubbing alcohol also. Useing my range rod with the proper size jag I soak patches in alcohol thenj place them on the jag and swap a few times and change patches till they come out clean. Once they come out clean I use a alcohol soaked cleaning towel to clean up and blow by. reassemble the bolt reinstall the breach plugs and nipple. When finished oil the bore and all other metal parts both the inlines and the side locks.
Not a thing wrong with the soap and water method in fact some of the cleaners on the market today for cleaning Muzzle loaders are so harsh you can strip a finish off a stock and discolor a tupperware stock. Extreame care should be used in their use.
I like to swab between shots with windex with alcohol added to it, evaportes quickly.

Al