water key

noun4

1. •
   A valve or tap for the drainage of accumulated fluid (saliva) from musical instruments such as trombones or trumpets.
2. •
   Any of several kinds of key (wrench) used to open and close water valves of certain kinds.
3. •
   A rod used to open and close a buried quarter-turn water valve, as in a water main.
4. •
   A sillcock key.