A bucket was a container used mainly to carry liquids.
In the spring of 2007, while facing a Hoix with the Tenth Doctor, Rose Tyler threw a blue bucket of liquid at the Hoix. This was the wrong bucket, Rose had thought the Doctor said blue, but as the Doctor noted, he had said "not blue". This enraged the Hoix who chased Rose and the Doctor until Rose found the correct red bucket. (TV: Love & Monsters)
In 2010, Clyde Langer threw a bucket of vinegar over a member of the Slitheen family. As it contained acetic acid, which could kill Raxacoricofallapatorians because of their calcium-based biology, it caused the Slitheen to explode. (TV: The Nightmare Man)
During the global afforestation of the Earth in the early 21st century, a minister broadcast a message telling people to fill their baths, sinks and buckets with fresh water. (TV: In the Forest of the Night)