A filter bag assembly includes a flexible bag bounding a compartment that is configured to hold a fluid. An inlet port and an outlet port are each secured to the flexible bag so as to communicate with the compartment. A porous filter sheet is disposed within the compartment of the flexible bag so that fluid entering the compartment through the inlet port must pass through the filter sheet before exiting the compartment through the outlet port. A first retention seal secures the porous filter sheet to a portion of the flexible bag within the compartment, the first retention seal having an outer perimeter edge that forms an annular continuous loop.