Multi-level drainfields for purifying septic tank liquid effluent have a plurality of vertically-stacked filtration medium layers with air space therebetween. The space-saving drainfield modules may be custom-fitted in size, number, type and thickness of layers to meet the requirements of a home, family and habits. Effluent may be percolated through each filtration layer, which may contain baffles, from top down or bottom up, in series or in parallel, and may be recirculated, if necessary, to render the effluent safe for discharge as clean ground water. Drainfield modules may be combined for high-capacity effluent handling, and may be installed underground or aboveground, where protective housing can permit light to reach the effluent therein.