A majority of the world's population use onsite sanitation systems, which store or treat excreta close to where it is generated. Sludge from these systems needs to be managed through a series of stages, known as the sanitation value chain. There is a huge diversity of service providers, not only within each part of the chain, but also along the chain bridging the different components. These service providers are linked not only by the flow of materials, but also by the transfer of money. Therefore for this system to be considered financially sustainable all services from the toilet to reuse or disposal need to be considered. A tool has been developed (eSOSView™) to simulate, evaluate, and optimise the financial flows along and within the sanitation value chain. In this paper eSOSView™ was tested, validated (using existing data), and piloted (including data collection). This paper demonstrates how eSOSView ™ can be used to evaluate different financial flow models, to assess financial sustainability in different parts of the sanitation value chain and optimise the financial sustainability along the sanitation value chain.