Thermo-solutal chimney-plume flows from a solidifying dendritic mushy region have been promoted in thin-walled glass tubes of internal radii from 0.3 mm–2.0 mm. Flow rates, liquid compositions and temperatures were measured as functions of the depth of immersion of capillary tubes in the advancing mushy region. The results demonstrate competition between buoyancy pressures and the restrictions of liquid recirculation within the dendritic array and have been analysed to provide permeability data for the mushy region at high liquid fractions. These data have been used to make some assessments of channel/plume dimensions for naturally occurring, unconstrained flows in the same system.