1
general::
Phrase(s): *slick as a whistle
quickly and cleanly; quickly and skillfully. (*Also: as ~.) • Tom took a broom and a mop and cleaned the place up as slick as a whistle. • Slick as a whistle, Sally pulled off the bandage.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Very smooth and neat; also, smoothly, quickly, easily. For example, That salesman is as slick as a whistle, or The fence post went in place slick as a whistle. The allusion in this simile, first recorded in 1830, is not totally clear, but presumably it refers either to the ease of producing a whistle or to its clear tone.
American Heritage Idioms