Home-based care facilities provide basic healthcare services to people too sick or frail to access formal clinics and hospitals. These facilities produce 'healthcare risk waste' which must be managed responsibly, and it is the work of Environmental Health Practitioners working within municipalities to ensure that the waste produced by home-based care facilities is managed in line with legislation. This paper presents a case study of a twenty-seven-month expansive learning intervention in a South African municipality that sought to transform its healthcare risk waste management practices. Limited knowledge and inadequate knowledge-sharing practices were identified as the main hindrances to effective waste management. The practitioner-researcher facilitated a series of inter-agency, formative intervention workshops with municipal employees and Community Health Workers using the Developmental Work Research methodology. These workshops strengthened both groups of practitioners' knowledge of the 'who, how, what, why and when' that underpins effective healthcare risk waste management, and enabled 'boundary crossing' for practitioners to work across their specialist areas towards co-defining and analysing problems and constructing new solutions.