Water heater glossary: definition of drain valve

More lingo:

Drain valves stretch over a wide scale of functionality and efficiency. They can be made of metal or plastic, open and close repeatedly or hardly at all, be expensive or dirt cheap. At left, you can see a brass spigot-type drain valve (red circle), mounted on a light commercial water heater, as well as two variants typically found on residential tanks, right. The top one is often called a cone valve, and opens and shuts by turning the large collar, while the bottom one is another spigot type.