There is a walkthrough here on simulating data in a workflow, this is likely how you would get your virtual trash cans to fill. You could have the levels rise over time by reporting the device’s last state and adding to it on a timer.
Instead of triggering a device command with your input block, you would trigger a workflow:
This workflow would empty your virtual device, returning it to a level of 0 whenever the button is pressed. You could do this for each trash can:
Then, on your dashboard, you will be able to see the levels of the device go to 0 on your bar chart.
Let me know how else I can help!
Julia