How do I see a graph of actual flow coming in and out of a tank?
The inflow and outflow results for a tank are the net inflow and outflow. To see the actual flow in the tank over the course of time you could graph the flow in the pipes adjacent to the tank.
The graph of 'Level (Calculated)' or percent full in the tank will also provide a visual indication of the filling and draining.
Modeling top fill tanks and throttling inlet valves
Rapid flow oscillation between hydraulically close tanks