This research addresses the critical issue of the poor implementation of sanitation and its effect on community and environmental health in the Global South. To overcome the social, cultural, technical, and financial complexities underlying poor sanitation, the participation of local community members in sanitation planning processes is deemed crucial for the successful development and implementation of sanitation systems. To engage local stakeholders as decision-makers and improve design freedom, it is proposed to engage stakeholders in determining their demands, needs, and priorities by combining the Fuzzy Analytical Hierarchy Process (FAHP) and Focus Group Discussions (FGD) as a participatory decision-making method. The applicability and suitability of this method are assessed through a case study in Hagonoy, the Philippines, in which two parallel design cycles are carried out: one with only local sanitation experts as decision-makers and one with only local community members as decision-makers. A systematic literature review of design criteria applicable to sanitation design processes was conducted to overcome selectors' bias regarding the decision criteria assessed in the FAHP and the FGD. The FAHP data was collected among 60 community members evenly distributed over six neighbourhoods in Hagonoy and six local sanitation experts. Three FGDs were held with local community members, whilst one FGD was held with local sanitation experts. The design cycle based on the defined design scope was limited to the development of a conceptual design, proposing a treatment train capable of treating the produced domestic wastewater such that the effluent satisfies the local General Effluent Standards, specifically for the parameters water volume, Total Phosphorus (TP), Chemical Oxygen Demand (COD), Ammonia (NH3), and Nitrate (NO32-). Wastewater treatment technologies aligning with the demands and needs specified by the stakeholders were obtained from scientific literature, which were combined into a sanitation system configuration that could treat the water sufficiently. The completion of a sanitation design process without predefining the possible solutions, but by integrating the FAHP + FGD in the systematic derivation of the design scope, demonstrated how a demand- and need-driven design approach allows increased flexibility and sensitivity for the context in the development of a design. The parallel design cycles showed how the FAHP + FGD method could be applied as a systematic procedure to understand how design criteria in sanitation design are preferred and interpreted differently between local community members and local sanitation experts and how this can influence the conceptual design. Altogether, this research contributes to the body of knowledge in community-engaged sanitation design by demonstrating the effectiveness of the FAHP and FGD method in engaging community members in a need-driven design process, overcoming selectors’ bias for technologies and trade-offs, and producing relevant design proposals. However, acknowledging that the FAHP + FGD method was limited to engaging stakeholders only in defining the needs and demands, verification of the designs’ alignment with the perspectives of stakeholders and continuous engagement throughout the entire design process is essential to be further researched in the future.