
As clean as a whistle
Metaphorical Use
The phrase is a metaphor, comparing something's cleanliness to a whistle's clear sound, not its physical state. 
Exaggeration for Effect
Often used to exaggerate how clean something is, implying it's exceptionally clean. 
Common Collocations
Commonly found with words like 'spotless' and 'sparkle' to emphasize cleanliness. 