Heavy-duty vehicles carrying liquids are subjected to higher instability than others due to sloshing phenomenon. In this case a vehicle composed by tractor and trailer is taken into account. When the tank is partially filled, the liquid tends to move, affecting the vehicle handling and stability. In this study the sloshing problem is analysed in Simscape environment, thanks to the "Simscape Vehicle Templates" model created by Steve Miller. The sloshing phenomenon have been represented with an equivalent mechanical model, in particular by means of pendulums. In order to run numerical simulations, sloshing parameters and functions have been written in Matlab. Moreover, to proper simulate real world, several manoeuvres have been considered. In this way transient and steady-state behaviours are analysed.