  Drain vortices are among the most common vortices observed in everyday life,
yet their physics is complex due to the competition of vorticity's transport
and diffusion, and the presence of viscous layers and a free surface. Recently,
it has become possible to study experimentally drain vortices in superfluid
liquid helium, a fluid in which the physics is simplified by the absence of
viscosity and the quantisation of the circulation. Using the Gross-Pitaevskii
equation, we make a simple model of the problem which captures the essential
physics ingredients, showing that the superfluid drain vortex consists of a
bundle of vortex lines which twist, thus strengthening the axial flow into the
drain.
