What is the term used for disposing of something by throwing it over the side?

The term "Deep Six" specifically refers to the act of disposing of something by throwing it over the side of a ship, often into deep water. This phrase has nautical origins and is used to mean disposing of items in a manner that they are effectively lost or forgotten, as "six feet deep" is a metaphorical reference to burial at sea. It embodies a practice historically associated with maritime operations where unwanted materials or waste were disposed of in the ocean.

In contrast to this term, the other options do not carry the same specific maritime connotation. "Sink" typically refers to something going below the surface of the water, but does not explicitly indicate disposal. "Cast Off" generally means to let go of something, especially in terms of ropes on a boat, and does not specifically denote disposal by throwing overboard. "Throw Away" is a broad term for discarding an item but lacks the specific connection to maritime practices that "Deep Six" possesses.