Retention of imported consumable stores: duty-free on board subject to Customs seal or inventory exception. Imported consumable stores arriving on a vessel or aircraft from a foreign port or airport may remain on board without payment of import duty while the vessel or aircraft is not foreign-going, provided alcoholic liquor and tobacco products are kept under Customs seal and other consumable stores are likewise sealed unless the proper officer, if sealing is impracticable, allows them to remain after taking an inventory.