We're removing all parts from the exterior of the Airstream in preparation for polishing. One of the parts we've removed is one that I'd never understood -- and still don't.
PICTURE 1: This part was attached to the outside aluminum of the rig with rivets just above the battery compartment. The first picture below shows what it looks like from the outside. (That's paper background, standing in for the aluminum.) You can see that it has a small shelf of sorts, hole in the center below. After cleaning out prehistoric gook, I discovered what appears to be a threaded inside.
PICTURE 2: On the inside of the exterior aluminum, the part has a nipple, to which is connected a plastic hose that leads down through the wall and into the battery compartment. There is nothing in the hose (except some dirt).
PICTURE 3: This is the part in profile as removed from the Airstream. (On edit, I just noticed that I reinstalled the hose upside down, so the aluminum part should be rotated 180 degrees.)
So what the heck is this?
PS: Please excuse the quality of that last pic. Obviously, I'm having trouble switching from a DSLR to a point-and-shoot.