It just happens that I recently brought a 1990 Honda VFR400R to enter into historic races.

During the process of cleaning the bike up I realised that the coolant reservoir had a bit of brown junk in the bottom in a position that was really hard to clean mainly because it was in a convoluted part of the bottle and hard to reach with a tooth brush Etc. My thinking was that it sort of needed tumbling with some sort of abrasive. Clearly, sand, metal, rocks Etc. would not be a good idea... As I was loading the dishwasher I noticed the rock salt and the solution was obvious

It works like a charm with a little bit of a shake and any residue just washes out. Works for me ...