  The iron-based superconductor FeTe$_{1-x}$Se$_{x}$ has attracted considerable
attention as a candidate topological superconductor owing to a unique
combination of topological surface states and bulk high-temperature
superconductivity. The superconducting properties of as-grown single crystals,
however, are highly variable and synthesis dependent due to excess interstitial
iron impurities incorporated during growth. Here we report a novel
physicochemical process for pumping this interstitial iron out of the
FeTe$_{1-x}$Se$_{x}$ matrix and achieving bulk superconductivity. Our method
should have significant value for the synthesis of high-quality single crystals
of FeTe$_{1-x}$Se$_{x}$ with large superconducting volume fractions.
