Fourteen super star clusters (SSC) sites are identified in the central bar of the external galaxy NGC 253, and the factors influencing their star-formation efficiency are considered. Molecular emission clearly shows red-shifted emission and blue-shifted absorption line profiles (P-Cygni) characteristic of outflows. While separation of large-scale motions in CO along the line of sight is difficult, CS and HCN are identified as tracing localised and spatially resolved emission within the clusters rather than the foreground gas. The SSCs are shown to fragment into primary clusters surrounded by smaller satellite clusters. From column density and projected sizes, outflow mass and other physical parameters are estimated, and outflow drivers and feedback mechanisms are discussed. The application of chemical clocks, particularly involving sulphur species, is explored and wider molecular comparisons made.