  We describe a simple dark sector structure which, if present, has
implications for the direct detection of dark matter (DM): the Dark Sink. A
Dark Sink transports energy density from the DM into light dark-sector states
that do not appreciably contribute to the DM density. As an example, we
consider 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 Dark
Sink by adding one to a DM freeze-in model in which $\chi$ couples to a light
dark photon $\gamma '$ which kinetically mixes with the Standard Model (SM)
photon. This freeze-in model (absent the sink) is itself a benchmark for
ongoing experiments. In some cases, the literature for this benchmark has
contained errors; we correct the predictions and provide them as a public code.
We then analyze how the Dark Sink modifies this benchmark, solving coupled
Boltzmann equations for the dark-sector energy density and DM yield. We check
the contribution of the Dark Sink $\psi$'s to dark radiation; consistency with
existing data limits the maximum attainable cross section. For DM with a mass
between $\text{MeV} -\mathcal{O}(10\text{ GeV})$, adding the Dark Sink can
increase predictions for the direct detection cross section all the way up to
the current limits.
