The application relates to a device and method for preparing and testing a fluid sample using a filtration procedure for analysis of a filterable constituent of the fluid. In particular the process employs an enclosed pathway whereby the fluid sample may be put into a sealable flexible containment-vessel, and can then be passed through a fluid passageway to a removable enclosable filter cartridge, wherein the filterable constituent may be removed and the resultant filtrate fluid discharged from the cartridge. Once introduced to the flexible vessel, the enclosed pathway system thereby enables the fluid to be filtered and the filterable constituent examined with minimal complications of contamination of the sample through exposure to environmental pollutant external to the fluid sample.A useful objective of the device and method is to enable analyses of microbiological content of a fluid sample.The application further relates to a means of conducting the filtration of a fluid sample without necessarily requiring a pump or vacuum equipment to express or aspirate the fluid from the flexible containment vessel through the filter cartridge.