(But now it's obvious
the pipe needs painting. Next job!)
Our oil tank's air vent (when oil goes out to the burner, air has to come in to fill the vaccuum) is a simple pipe that runs up the side of the house, with an open top for the rain and pine needles to fall in. There must have been a cap on it when first built, but that was back in the 1940s - who knows what happened to it. I could of course spent a little money for an official cap, but the requirements are simple: air-permiable, rain-resistent, and possessed of character.
A busted flagpole supplied me with an eagle topper that fit the pipe nicely, but I wasn't absolutely certain about the passage of air. I drilled a horizontal shaft back to front (this will be invisible when mounted since the ornament is above eye level) and then a vertical shaft from the base up. An air test (blowing through the bottom) showed that the vertical shaft debris clogged the junction but it was easy to ream out.
In progress ...
...a simple mod
In place it looks fine: a little bit idiosyncratic, but isn't that the point? One dollar saved, one item kept out of the land fill, and one minor task accomplished!