Over 25 years ago, Brown and Duguid ("Organisation Science," 2(1), 40-57, 1991) highlighted the differences between the way organisations formally describe and delineate jobs and the actual practices of their employees. This paper combines ideas from their seminal contribution with theories of "job crafting" and identity to examine the agentic behaviour of employees in low-grade, "dirty work" as they utilise their expertise and practices to (re)frame their occupational identities and challenge their prescribed job boundaries. The evidence for the paper comes from a qualitative study of hospital porters in the UK's National Health Service. It argues that this combined theoretical approach provides a potential research and employment framework to challenge the abstracted and stereotypical conceptions of the expertise related to low-grade jobs.