An apparatus, such as a flow restriction apparatus, is provided. The flow restriction apparatus includes an ink outlet perforating through a tank wall of a printing fluid reservoir of a user-refillable inkjet printer system. The ink outlet facilitates fluid communication between the printing fluid reservoir and an inkjet pen of the printer system. Printing fluid from the printing fluid reservoir enters the ink outlet from the printing fluid reservoir under suction pressure exerted by the inkjet pen. A screen is located inside the printing fluid reservoir and separates the printing fluid reservoir from the ink outlet. The screen is ink permeable. The screen includes a screen aperture having an effective radius smaller than a meniscus of a droplet of printing fluid at atmospheric pressure within the printing fluid reservoir.