bilge water
淦 refers to bilge water, the dirty water that collects in the bottom of a ship.
淦 combines 氵 (water) with 金 (metal, gold). The exact historical development is uncertain, but it likely relates to water associated with metal or gold, possibly referring to the metallic-tasting or dirty water found in a ship's bilge.
Picture water 氵 mixed with metal 金 filings or rust, creating the dirty bilge water that collects at the bottom of a ship.
For カン, imagine a can of bilge water: can -> カン, and the can is full of the dirty water from the ship.