An aspirator cassette includes a housing having first and second ends sealed off by first and second end caps, respectively. A partition mechanism is enclosed within the housing for dividing its internal volume into first and second regions. First and second fluid flow ports are mounted on the first and second end caps, respectively, to provide fluid flow paths into and from the first and second regions, respectively. When the first region is filled with liquid, its associated first port is connected to a vacuum source for sucking the liquid out of the region, whereby as the liquid is removed, the partition mechanism responds by decreasing the volume of the first region, and increasing the volume of the second region causing its second port to draw a vacuum for sucking fluid from an aspiration device connected to the second port.