Final answer:
The phrase "This house is as clean as a whistle" is an example of a simile.
Step-by-step explanation:
The phrase "This house is as clean as a whistle" is an example of a simile. A simile is a comparison that uses like or as, and in this case, it compares the cleanliness of the house to the purity of a whistle. It is not a metaphor, which directly compares two unlike things, and it does not have any connotations attached to it.