There was a brass rod, shaped much like a large hook, that went thru the cork vertically. The hook projected out the bottom and curved forward.
When the overflow pipe was in the lowest position in the cylinder, the hook would be against the bottom of the cylinder bowl and push the cork upward, exposing the words "to storage". Once that pipe was lifted into position for filling cylinder, the weight of the cork with the brass hook would pull the cork downward exposing the words "to car".
Filling cylinder with fuel would float the cork and again expose "to storage" once fuel reached capacity.
Sorry, I don't have photos.