Wash'Em is a process that supports humanitarians in assessing and designing rapid but context-specific hygiene programmes in crises or outbreaks. The process consists of training implementers, using tools to learn from populations, and entering findings into a software which generates contextualised activities. A process evaluation of Wash'Em use was conducted in a drought-affected area in Midland province, Zimbabwe. Data were collected during the programme design and following implementation using a mix of qualitative methods. Findings were classified against the intended stages of Wash'Em, and the evaluation domains were defined by the UKRI Medical Research Council. The Wash'Em process was not fully implemented as intended. An abridged training was utilised, some of the tools for learning from populations were omitted, many of the recommended activities were not implemented, the delivery modalities were different from intended, the budget available was minimal, and the number of people exposed to activities were fewer than hoped. Despite these 'on the ground' challenges and adaptations, the Wash'Em process was considered feasible by implementers and was seen to be less top-down than most programme design approaches. The populations exposed to the intervention found the activities engaging, understood the content, and reportedly took action to improve handwashing behaviour. Programmes such as Wash'Em, which facilitate community participation and are underpinned by theory and evidence, are likely to yield positive results even if processes are followed imperfectly.