Suspect bathroom breaks
When taking a subject to the bathroom, handcuff their dominant "strong" hand behind them to their belt or belt loop and uncuff the non-dominant "weak" hand. This may help prevent evidence from being easily retrieved and thrown down the toilet.
This was a lesson that I learned just this week when a suspect, thanks to the free use of his dominant hand, retrieved and flushed contraband down the toilet very quickly before I was able to get to it in time. He had pushed me out of the way.