A housing defines a fluid reservoir for an imaging device. One or more exterior walls define a volume for holding ink to set a fluid backpressure in the imaging device. An opening in the walls is positioned for overflowing excessive ink from the volume to maintain the fluid backpressure within a predetermined operating range. Fluid inlets and outlets connect the reservoir to both a supply item and an ejection head. Ink flows into the reservoir from the supply item. It fills until the fluid rises to a height where it overflows back to the supply item. Less full reservoirs fill as the pump operates, while full reservoirs simultaneously return fluid back to their supply containers. Fluid does not spill from the walls.