petcock
/ˈpɛtkɑk/
noun
- A small valve or faucet used to release pressure or drain liquid from a pipe, engine, or container.
- The mechanic opened the petcock to drain the old oil from the engine.
- Before winter, you should close the petcock on the outdoor water spigot to prevent freezing.
- The radiator has a petcock at the bottom for flushing out the coolant.