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We describe a simple dark sector structure which, if present, hasimplications for the direct detection of dark matter (DM): the Dark Sink. ADark Sink transports energy density from the DM into light dark-sector statesthat do not appreciably contribute to the DM density. As an example, weconsider a light, neutral fermion $\psi$ which interacts solely with DM $\chi$via the exchange of a heavy scalar $\Phi$. We illustrate the impact of a DarkSink by adding one to a DM freeze-in model in which $\chi$ couples to a lightdark photon $\gamma '$ which kinetically mixes with the Standard Model (SM)photon. This freeze-in model (absent the sink) is itself a benchmark forongoing experiments. In some cases, the literature for this benchmark hascontained errors; we correct the predictions and provide them as a public code.We then analyze how the Dark Sink modifies this benchmark, solving coupledBoltzmann equations for the dark-sector energy density and DM yield. We checkthe contribution of the Dark Sink $\psi$'s to dark radiation; consistency withexisting data limits the maximum attainable cross section. For DM with a massbetween $\text{MeV} -\mathcal{O}(10\text{ GeV})$, adding the Dark Sink canincrease predictions for the direct detection cross section all the way up tothe current limits.

A Dark Sink Enhances the Direct Detection of Freeze-in Dark Matter