Pipeline physics astound me: the same single pipe can be used for a series of different products with only a small boundary volume between them needing to be diverted [0]. As a naive software guy I would have feared that across 170km and numerous valves and pumps cross-contamination would become problematic, but apparently not so (plus the definition of the fuel types had greater tolerances than laboratory-grade chemicals)

[0] https://channelnz.com/what-we-do/terminal-pipeline-services/....