A vessel (10) and a method for agitating a liquid (50) in a main cavity (16) of t he vessel (10), are provided. The vessel (10) includes a dividing member (40), extending deformable pump cavity (20). To agitate the liquid (50), a user presses a flexing wall (26) of the pump cavity (20), in pumping cycles, to discharge liquid from the pump cavity (20) through nozzles (42,44) into the main cavity (16). The dividing member (40) has a sloping upper surface, which causes additives (38) to collect in the region of the nozzles (44), to be agitated more effectively.