The creation of functional nanostructures by electron-beam-induced deposition (EBID) is becoming more widespread. The benefits of the technology include fast 'point-and-shoot' creation of three-dimensional nanostructures at predefined locations directly within a scanning electron microscope. One significant drawback to date has been the low purity level of the deposition. This has two independent causes: (1) partial or incomplete decomposition of the precursor molecule and (2) contamination from the residual chamber gas. This frequently limits the functionality of the structure, hence it is desirable to improve the decomposition and prevent the inclusion of contaminants. In this contribution we review and compare for the first time all the techniques specifically aimed at purifying the as-deposited impure EBID structures. Despite incomplete and scattered data, we observe some general trends: application of heat (during or after deposition) is usually beneficial to some extent; working in a favorable residual gas (ultra-high vacuum set-ups or plasma cleaning the chamber) is highly recommended; gas mixing approaches are extremely variable and not always reproducible between research groups; and carbon-free precursors are promising but tend to result in oxygen being the contaminant species rather than carbon. Finally we highlight a few novel approaches.