The embodiments disclosed herein relate to methods and apparatus for promoting bubble-free circulation of processing fluids in a recirculation system. Certain disclosed techniques involve passive, mechanical valve designs that promote variable resistance to flow in a drain. Other techniques involve automated flow control schemes that utilize feedback from flow meters, level sensors, etc. to achieve a balanced and bubble-free flow. The disclosed embodiments greatly reduce the incorporation of gas into a processing fluid, in particular as the processing fluid returns from a processing cell to a reservoir.