The publication introduces the Waste Flow Diagram (WFD) as a tool with the aim to provide a rapid assessment methodology for mapping waste flows in a municipal solid waste management system, including quantifying the sources and fate of any plastic pollution. Main objectives are 1) to enable a rapid assessment of a municipal solid waste management system and to visualize waste flows, 2) to use observational-based assessments to quantify the sources of plastic leakage into the environment from the municipal solid waste sources and determine the fate of this uncontrolled waste, 3) to identify the high-priority sources of plastic pollution to delineate suited interventions, 4) to allow benchmarking and comparison between municipal waste systems, 5) to run scenarios to gain approximate insights into how proposed interventions may impact and enhance the solid waste management system and reduce plastic pollution, and 6) to quantify the effectiveness of applied interventions.