Bilmaly
Let me respond first in general. There is no difference between cleaning a sidelock or an inline, other than the physical differences between them (i.e. removable breachblock or not). Black Powder and Pyrodex, as mentioned earlier, are both water soluable, so anything with water in it will do an adequate job. The reason hot water is recommended has nothing to do with disolving the residue, it heats the barrel, causing the barrel to dry more quickly than cold water will. Cold water will do an adequate job, as will urine or anything else handy that has a high proportion of water.
General advice I have read over the years suggests avoiding the use of H2O2, or Hydrogen Peroxide, as way too aggressive. I had no problem using it, but then I dried and oiled my barrels immediately after cleaning, and I can see the problem for those who don't follow this practice. I quit using it because it's simply unnecessary. I've gone to water with a little soap in it, because I'm shooting a BP Cartridge gun and I have the soapy water there to drop my fired cartridges in, it's easy to soak a patch and run it through the bore. There's no great virtue in the soap except that it helps loosen residue in the cases with little agitation.
As to plastic, I have no experience with plastic residue, but would think a good brushing would take care of it. If not, there are products on the market that will dissolve it.
Don't get overly worried, almost anything on the market designed for black powder will work. If all else fails, drink some water and spit on a couple of patches!