This is the website that the image is from: http://www.motherearthnews.com/renewable-energy/other-renewables/biogas-generator-zm0z14aszrob (Manure goes through the feeding tube, then anaerobic bacteria produces methane. The methane then goes to the second tub and is collected)
On the right side of the diagram,
why does the barrel need to be immersed in water? Does it do something to the methane?
why does the methane not immediately go from the first tank through the tube out to the burner but instead goes into the second tank?
Once the methane is inside the second tank, what's stopping it from rising and going out?