Core material is removed from a passage in a casting by exposing at least a portion of the core material in the passage to a leaching liquid. At least a portion of the core material in the passage is exposed to a gas. An opening to passage is exposed to a gas. At least a portion of the leaching liquid in the passage is boiled while the opening to the passage is exposed to a gas. At least a portion of the leaching liquid is expelled from the passage in the casting by the boiling action. To expose at least a portion of the core material in a passage to a leaching liquid, a flow of leaching liquid is conducted from a reservoir container to an operating container in which the casting is disposed. To expose at least a portion of the core material in the passage to a gas, a flow of leaching liquid is conducted from the operating container to the reservoir container.