After you have made your wash,you need to use a large flat Bush,and brush it over the tank,The gray primer coat that you used will be the high lite on the model.Let the tank dry on a flat surface so the green wash will settle in all the detail. This method works will for looking the right scale.Paint 2 coats of this wash,to get the right color.
Next I will so you how to paint the black camo pattern.