urn
缸 centers on a container for liquids or solids: an urn, a jar, or a vat. The single given meaning 'urn' is the core idea.
缸 combines 缶 (a jar or earthenware container) with 工, which likely contributes the sound. The character originally referred to a large earthenware vessel.
The left side 缶 is a jar, and the right side 工 looks like a sturdy stand. Picture a large urn resting on a stand: 缸 is an urn.
For コウ, imagine a coal urn: coal -> コウ, and the urn holds glowing coals.