Dear FlyingCamera:
You probably already realize this: One spigot has a 'hard' gasket or washer for the pour-in hole on top - it's shinier. The other spigot has a 'softer' gasket that better seals the lower pour-out hole on the side - and it is dull in appearance. If they are switched - easy to do - the lower spigot will leak. Perhaps take a look at the difference: The duller, softer, washer belongs on the lower-side as the out-flow spigot.