From King Dictionary of Contemporary English
Related topics: Technology, Household
ballcockball‧cock /ˈbɔːlkɒk $ ˈbɒːlkɑːk/ noun [countable] TDHa hollow floating ball on a stick that opens and closes a hole to allow water to flow into a container, for example in a toilet
Examples from the Corpus
ballcockAutomatic top-up with a ballcock will allow all water in a new pool to pass first through the Eradicator.It had Hayley Syndrome-a missing ballcock.Meanwhile, I had to go up into the roof and push down the ballcock when things went wrong.