Seacock

A seacock is a valve on the hull of a boat or a ship, permitting water to flow into the vessel, such as for cooling an engine or for a salt water faucet; or out of the boat, such as for a sink drain or a toilet.

The reason for this is that when the boat is level, the drain or other opening will always be above the waterline, and so water will only flow out.

If the seacock is open, water may flood the boat, causing it to sink.

Typically, this is done to magazines to prevent detonation of the ammunition in the event of fire, such as the case with HMS Glatton or to maintain trim due to battle damage (counterflooding).

[2][3] The Royal Yacht Association recommends that replacement sea-cocks for recreational vessels should nowadays comply with ISO 9093-1.