Reverse Logistics is now considered as an interesting source of economies in supply chain management. Through different activities, this logistics has received increasing attention from researchers and practitioners. In this paper, we are interested in a tactical problem by focusing on the optimization of return flows of reusable containers, while considering an existing network. This situation is very encountered by third part logistics companies. The optimization model we propose is a MILP which minimizes the total cost of these return flows. In order to be realistic, we want to use this model on large size networks. The key point is the computation time which exponentially increases with the size of the problem. A simple heuristic is also proposed in order to reduce this computational time. Finally, a numerical experiment is presented to demonstrate the performance of the developed model as well as the efficiency of the proposed heuristic.