We present a model for plasma transport in a rotation-dominated magnetosphere (e.g., Jupiter) containing an internal plasma source (e.g., Io). We make a distinction between magnetic flux tubes filled with outward moving plasma and less dense flux tubes that move in to compensate. In the outer region where the heavier tubes are effectively isolated, their motion is described by a pair of coupled differential equations which have analytic solutions in the small velocity approximation. In a steady state, conservation of flux-tube plasma content requires that the fraction of mass-loaded flux tubes be a function of the radial outflow speed. Similar equations govern the motion in the inner region where heavy flux tubes predominate and lighter tubes are isolated. This raises the possibility of net outward radial transport even when the radial gradient of average flux-tube content is positive. In the outer region where heavy flux tubes are isolated, the average steady-state flux shell content decreases outward as the inverse square of radial distance.