A method of priming an inkjet printhead having ink ejection nozzles. The method includes: providing an ink bag containing ink for distribution to the nozzles via a fluid path between the ink bag and the nozzles; applying inwardly directed force on at least one exterior wall of the ink bag so as to reduce an available fluid volume of the ink bag, thereby causing ink to flow from the ink bag to the nozzles along the fluid path; and arranging a biasing member in the ink bag so that the biasing member applies outwardly directed force on at least one interior wall of the ink bag to restrain the reduction of available fluid volume of the ink bag only once the available fluid volume of the ink bag has been reduced to a predetermined volume. The printhead is a pagewidth printhead, having a pagewidth of 100.9 millimeters.