No leaks, no mess. Collect approximately 300 live bees into one side of the shaker. Into the other side pour 1 cup of blue windshield washer fluid. Swirl bees in solution for 1 minute to remove all mites. This will give you an accurate mite count. You can also use with powdered sugar for a slower result, but still accurate.
This is a must have tool for mite monitoring, every beekeeper should have one as part of regular IPM routine.