Smoking the scraped black resin is a bit odd cause it has a harsh taste, similar to half-assed honey oil or those other leftover chemicals you might taste in something homemade and think "I shouldnt be tasting this". Any nonpolar solvent should take the crap right out but rubbing alcohol has, for me anyway, tried and true worked the best and the fastest. Ethanol or vodka is slower and ether, although it should in theory work the best, barely works at all (was not 100% pure ether). Stick to isopropanol. Haven't tried salt but a pinch is all you'd need and that should help react stickier compounds, although I'd rinse it well afterward.

Alcohol (ethanol, methanol, or isopropanol) is one of few substances that will completely evaporate if pure or near pure with water added (i.e. 90% rubbing alcohol is 10% water). Anything with molecules dissolved in it will theoretically leave residue other than just undissolved resin that was there to begin with. Potassium is never a pure ingredient since it hates being in that state (much like sodium... they can just spontaneously combust), but it can make lots of salts, just like table salt would if not more. Without a very good solvent rinse afterward (like with rubbing alcohol), it'd be a bad idea. There are other things besides potassium or lye in commercial cleaners that make them very bad choices. Stick with the cheapest and best. Warning: only use on metal and glass.

Edit to say you can just buy a bottle of rubbing alcohol with a suitably large cap, drop the piece in, shake it around, pull it out a few hours later, and reuse the liquid in the future... if not just put a bit in a small glass and soak/stir your piece for a few hours. Keep away from flames even though its not very dangerous as far as solvents go, better safe than sorry. If you add salt you will want to rinse it out again with fresh, non-salted alcohol. rinse well with water and air dry only. Can also rub a pipe cleanr inside while its in the alcohol, works well.