We analyze a single-electron transistor composed of two semi-infinite one-dimensional quantum wires and a relatively short segment between them. We describe each wire section by a Luttinger model, and treat tunneling events in the sequential approximation when the system's dynamics can be described by a master equation. We show that the steady-state occupation probabilities in the strongly interacting regime depend only on the energies of the states and follow a universal form that depends on the source-drain voltage and the interaction strength.