An inverted (air purged by pushing the tank down with the drain plug removed) 6 foot diameter poly stock nesting in a 9 foot diameter poly stock tank filled with water and kitchen garbage makes a do-it -yourself unit that might give you about 60 therms/day of 600 BTU/ft^3 methane, John. :-)
A plastic film for sealing the gap between the tank perimeters keeps odors in and the flies out.
The gas is piped from the drain port after the tank fills and rises.
Styrofoam insulation required of course.
Frederick
