Simplified sewerage provides an improved alternative to single user on-site options in peri-urban areas in India, and contributes to the aim of reducing the need for human handling of waste (manual scavenging), and the Government's goal of making India open defecation free by 2019. This research develops a mixed methodologies approach to design, optimise and assess failure risk for a proposed installation in a village in India. A steady state simplified sewerage model was used to do the initial design which was further modelled in DRAINET, a numerical model traditionally used for building drainage systems. The input data for DRAINET were obtained from a detailed survey carried out on site, which included usage pattern and focus group data. A total of 106 properties were included in the design and the survey. Test runs were carried out for the whole site over a 12-hour period. All main pipe runs were 100 mm diameter and set to a gradient of 1:100. A risk model was developed and applied to the DRAINET results which confirmed that the design operated effectively; however, there were areas of concern at the extremities of the site, which required additional flow boosting devices or gradient changed.