Cleaning between tumbling stages properly, and why it is not optional

Between every single tumbling stage, the barrel, the lid, and every individual stone need a genuinely thorough wash, not a quick rinse. Grit particles are small enough to hide in surface texture, in the barrel's seams, and under the lid gasket, and even a small amount carried into a finer grit stage will scratch the entire batch and can ruin what would otherwise have been a good polish. A stiff brush and running water, done stone by stone rather than just rinsing them as a group in the barrel, is the reliable way to do this. Many experienced tumblers keep separate barrels dedicated to a single grit stage specifically to remove any chance of cross-contamination entirely.