For the setup to be stable, the site where you are placing the drums has to be firm and dead level.

The small drum is filled with boiling water and jars till the surface of the liquid is just 3-4cm from the top of the drum so if there is any lean on the small drum, there is the risk that something will tip. As I live in town on a hill I have dug a small, circular depression in the back garden, used a spirit level and a small plank to make it flat and then bricked it over.

This is done in our backyard