I only used the word corrosive in response to your question about shooting corrosive powder through the can which I took to mean black powder or Pyrodex
that contain sulfur and produces sulfuric acid and other corrosives..
It's my understanding that moisture and the oxygen in it is what causes corrosion & oxidation

I really don't know anything about BH209, but since it's recommended to use an oil based solvent to clean it as you say, perhaps that's why they recommend warm and then hot water to
flush it out since the Maxim company must believe that it's at least partially effective.in flushing out some carbon deposits & particles that can absorb moisture or clog the baffles in the can.

Perhaps the metal in the can is made out of high quality rustless stainless, the kind that pots and pans are made out of, or another rustless aerospace metal?
And there may be cheap solvents that can also be used to help flush out the can, such as alcohols, cheap water based degreasers, water soluble cutting oil, natural citrus cleaners, Pine Sol, Mean Green or such.
There's even steam cleaning wands or pressure washers.
Spray it with some Fantastik and then take it to the do it yourself car wash... :-)
I'm just guessing because there must be a reason that Maxim recommends flushing it out so often with plain heated water..
If it's flushed out often enough, then perhaps the carbon residue never has much of a chance to accumulate to significantly interfere with its operation..

Since BH 209 is a nitro based powder, there's probably not any traditional creosote residue that would be produced as a by product as if it had contained charcoal as a fuel.
I wouldn't be too concerned about it since I don't plan on buying one.
I am trying to think of how I would thoroughly clean it if I owned one.
But they could have recommended another bulk solvent and cleaning procedure instead of simple water flushing if they thought that it was really necessary.
They could have designed the can with a built-in cleaning port
It may indeed have a special advanced design or materials that makes it so expensive.

Maybe the can will eventually get filled up with enough Black Horn goo to blow up the shooter? LOL!
Even though I thought that BH didn't create much goo to begin with...