We continue our construction of a hydrodynamical description of a holographic
model with broken translation invariance. Using the fluid/gravity
correspondence we derive the constitutive relations of the boundary theory in
the presence of a magnetic field. This allows us to obtain novel results for
the low-frequency magnetothermoelectric response coefficients. We discuss the
DC limit of our hydrodynamics in detail, and show that our approach is
equivalent to the `horizon-fluid' of Donos and Gauntlett.Comment: 16 pages + appendix and references, v2: references adde