The jug is a junk item in the Fallout 4 add-on Far Harbor.
The jug, which has the appearance of tarnished brass, is a component of the fog condenser used to gather condensed fog. The jug sits at the bottom of the condenser with a collection tube feeding in.
The jug can be broken down into its individual components for use in crafting:
Four can be found on the bottom level of Acadia.