This paper utilises the two-dimensional finite difference package FLAC to investigate various factors affecting mine drainage including the effects of anisotropy, ancillary drainage and geometry on flow through hydraulic fill mine stopes. The numerical modelling carried out using FLAC shows that the horizontal ancillary drain provided at the bottom of the stope reduces the pore water pressure at all points within the fill substantially, however large the stope is, with the reduction being proportional to the length of the drain. For the case of stopes with horizontal ancillary drains at the bottom, a simple expression was developed to predict the maximum pore water pressure that always occurs at the bottom corner of the stope. The ancillary drain increases the hydraulic gradient and thus the rate of flow, resulting in quicker drainage of the stope. It was also shown that anisotropy in permeability of the fill material could also lead to a substantial reduction in pore water pressure. An increased knowledge of the factors affecting drainage will provide an increased level of confidence in design, more efficient mining procedures to be developed, and safer filling practices to be undertaken.