A bucket was a container used mainly to carry liquids.
In the summer 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 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)