To efficiently remove valuable minerals from large scale underground mining operations, the orebody is often divided into a series of stopes. The stopes are blasted, the rock removed for processing, and the large void created is backfilled with a slurry made from the by-product of the mineral processing activity. Underground failures have occured as a result of poor drainage of excess water from the backfill. The permeability of hydraulic fill is typically between 10-30 mm/hr (much less than industry specification), and yet many mines using these fills have operated successfully for many years. Hydraulic fill typically settles to a porosity value between 37% and 48%, and the dry density may be approximated as 0.56 times the specific gravity. This paper discusses current developments in drainage analysis of hydraulically placed mine fill and fill barricades from four Australian mines.