The plain bucket in which the shapeshifter Odo rested in his liquid state during the early years of Deep Space Nine, before he took quarters of his own.
As a Changeling, Odo must return to his natural gelatinous form at regular intervals to regenerate. Having been raised in a laboratory, he knows no better way of doing so than pouring himself into a bucket kept in the security office.
The bucket is seen or mentioned in several early Deep Space Nine episodes, and Quark teases him about it. In The Forsaken, trapped in a turbolift with Lwaxana Troi as his cycle runs out, Odo is forced to revert in front of her, and she holds him in the folds of her dress.
In The Abandoned he shows Kira the quarters he has taken, where he can practise shifting freely. He keeps the bucket only as a reminder, and uses it as a pot for the plant she brings him.