The third world ones I have seen are a round dike with membrane cover, sealed around the edges with more dirt. Gas pressure holds the membrane up off the feedstock. The gas from the manure is collected under the membrane and exits via a central "rubber" hose that runs to the appliance. When production falls off you uncover and stir the shi* and put the cover back. Fires stoves, mantle lanterns, etc.

Way back in the 60's there was a high school teacher at Carlsbad, CA who fueled his daily driver commuter car (short drive on surface streets) with chicken manure. He lined the trunk with plastic sheeting and gave a whole new meaning to "fill 'er up." When production fell off he'd hold his breath, open the trunk and stir the shi* and close the lid. I don't recall how long he went before having to need new "charges" of "chicken power."

Pat