A collector may shake the specimen for the purpose indicated in the DOT Collector Guidelines (Jan 2018) with the assumption that they know what they’re looking for (they’ve had training to distinguish the differences) – and they should do so only when it is in a sealed container.  Shaking might indicate
Monitored Collections DOT If you use a multi-stall restroom, you must either: Secure all sources of water and other substances that could be used for adulteration and substitution (e.g., water faucets, soap dispensers) and place bluing agent in all toilets or secure the toilets to prevent access; or Conduct