Has anyone seen video of a clown playing a tin coffeepot?
Not that I can think of, though it sounds plausible. But I do know of 1920's kazoo bands playing coffee pots, like the "coffee-pot band" Deek Watson (later of the Ink Spots) joined in Indianapolis in the mid-20s. They were called the "Percolating Puppies" and used coffee pots as sound chambers for their kazoos.
Deek Watson mentioned that his band also included a small teapot, along with the coffee pots, and guitars and, coming (ever-so-slightly) back on topic for a moment, there's also a British Pathé (silent) newsreel from 1929 of a women's kazoo band, called the "Kitchen Cabinet Band", that includes a teapot and a coffee pot: The Kitchen Band!
And there's an article in Popular Mechanics, August 1927, about the "Kitchen Kabinet Band", its history, and its instruments: Kitchen Kabinet Band