A collapsible vessel for containing fluid comprises at least two interconnected tubular sections which are configured to move axially with respect to each other upon application of a substantially axial force thereto. The vessel is manipulatable between a collapsed configuration in which the sections are substantially nested to form a tube having a first length and an extended configuration in which the sections form a continuous tube having a second length which is greater than the first length. The vessel comprises locking means configured to be reversibly locked while the vessel is in the extended configuration upon the application of a rotational force to at least one section.