On-site sanitation solutions are an economically feasible method of improving sanitation, and for reducing the burden of diarrhoeal diseases, in low- and middle-income countries. However, suitable faecal sludge management (FSM) solutions are severely lacking in these countries. Black solider fly larvae (BSFL) efficiently reduce food-waste and animal manure, and produce valuable prepupae, high in protein and fat, supporting investigation into a novel BSFL FSM method. The aim of this study was to determine the feasibility of using BSFL as a FSM method, by evaluating their faecal matter reduction (FMR), and prepupal production capacity, when reared on FS under different conditions. Black soldier fly larvae were found to develop successfully on fresh human faeces, effectively reducing waste and converting it to prepupal biomass. A survey of pit latrines in South Africa found physical and chemical characteristics of faecal sludge (FS) similar to previous studies in countries requiring novel FSM methods, with characteristics falling within a range suitable for BSFL development. Key rearing parameters, moisture content, feeding rate, and larval density, significantly influence FMR and prepupal production of BSFL reared on “top layer” homogenised FS. Black soldier fly larvae were found to effectively reduce FS from a variety of depths, each with a range of physical and chemical characteristics, and produce prepupae with nutritious values comparable to previous research, excepting crude fats. The study also demonstrated that reported cleaning chemicals in FS do not affect BSFL mortality at manufacturer recommended, or user reported concentrations. It is proposed that the use of a novel BSFL FSM method is an economically feasible method of improving sanitation in low- and middle-income countries, and may help reduce the burden of diarrhoeal diseases.