A practical example of the use of single‐structure diffusion pumping groups in an experiment requiring hydrocarbon‐free, ultrahigh vacuum is presented. With the use of proper vacuum procedures and careful foreline design and operation, but with no exotic hardware or liquid nitrogen, we have demonstrated that such a pump could provide vacuum that was ‘‘clean,’’ i.e., which had no residual pump‐oil contamination to a partial pressure below 10−8mbar. Their use is thus compatible, at least in peripheral vacuum chambers, with standard ‘‘UHV‐surface science’’ processes. We discuss our vacuum system in detail, and present a review of the literature on the production of clean vacua with diffusion pumps.