This paper will first discuss the fundamental requirements for reliable discharge of backfill by gravity alone at high per cent solids. This discussion will include brief mention of the underlying principles of saturated solids flow contrasted to that of stirred tank or dilute discharge systems. Here the need to possess full knowledge of the flow properties of the stored material will be highlighted. In regard to attainment of reliable discharge it will he revealed flow from a backfill silo will only occur provided:_x000D_
the flowing material in the converging channel is yielding throughout;_x000D_
slip is occurring along the walls;_x000D_
an arched stress field is present in the vicinity of the outlet;_x000D_
the flowing backfill must be dilating to flow in response to the dilating stress field;_x000D_
sufficient dilation water is injected, in the hopper, to eliminate the formation of adverse interstitial pressure gradients;_x000D_
sufficient dilution water is injected, downstream from the hopper outlet, to generate a pumpable slurry of maximum per cent solids;_x000D_
the silo level must be sufficient to prevent the pump suction forming a rathole;_x000D_
the system must be configured and operated to generate stable discharge density; and_x000D_
the system must be configured and operated to minimise damage to the pump liners. In addition proper account must be made of the silo overflow weir and settling capacity to match plant throughput. Here opportunity will be taken to highlight the complexity of this multi-phase flow situation as well as the general yet paramount requirements for reliable solids flow. It will be shown that by proper attention to the multi-phase considerations gravity discharge of slurries as a consolidated bed with minimal water content is possible. Such high solids discharge results in greatly reduced demand for process water. In addition pumping costs are reduced as is the delay time associated with the mine drainage operation. Confirmation of successful applications will be highlighted by reference to several recent case studies. In the concluding phase mention will be made of the key yet very simple and effective operation techniques which enhance reliable Discharge.