A way to deal with the problem of surpluses of animal wastes is to implement collective treatment units. With aim to avoid stock overflowing and get some guarantee on the regularity of supply, this paper considers two questions: When should a delivery be done? How much has to be delivered? Based on an Hybrid Dynamical System approach (i.e. with continous and discrete-valued variables), we developed a model to answer these questions by simulating various management policies and optimizing control parameters. After describing this model, we show on an hypothetical case, involving 5 pig farms and 3 management policies, how it can be used to determine, for each farm, the dates and quotas of slurry deliveries and, further, to improve the overall system organization.