For many years, I researched and observed several different bio-gas system designs. Most of them required sophisticated engineering skills, loads of concrete, reinforcing steel, bricks and other expensive and time consuming inputs. On the other hand, the cheaper simple systems made with giant plastic tubes, were prone to fail regularly. I came across a system outlined in the PDF file attached below, that looked ideal, aside from the concrete steel and engineering skills needed, not to mention the man-hours and $s required to build it. In my suburban backyard, I started to experiment with recycled plastic containers and salvaged plumbing bits scavenged from roadside throw-outs. After several failed attempts, success was achieved by using a recycled 1 cubic metre plastic IBC tank I paid $20 for. This became the substitute for the digestion tank, that in the PDF file is an expensive, complex, brick and concrete construction. After 4 years, the simple gate valve at the bottom of this tank has now failed, so I am no longer able to desludge the tank which has now reached the level of the overflow pipe. I recently purchased a 2nd hand UV resistant black plastic IBC with a good solid ball valve at the base. It looks indestructible. I'll replace the old white plastic unit with this one, seen in the pic. After fitting the overflow/outlet pipe to catch the processed fluids, and an outlet pipe for the methane gas, a recycled toilet pan found on a roadside throw-out, was fitted to the top of the IBC. You are now ready to produce gas. Simply run the half inch poly pipe from the IBC tank, into a gas storage bag. A queen size air mattress that has a light weight cover on top of it to provide a gentle gas pressure for cooking does the job nicely. An old internal door and some plywood on the top of it did the trick. The airbed was put into the loft above my garage workbench area. The only glue/sealant that will work properly on plastic, is '3 in 1' by Selleys. Silicone does not work. Sewer plumbing fittings were used for inlet and outlets and if you lived in a high-set house with septic tank below, I see no reason why you couldn't put the IBC digestor between the loo and septic tank. In my situation, I have sewer mains connected to my household toilet so am not in a position to try this. So I use animal manure, urine and food scraps made up into a slurry, to feed the IBC tank digestor. The outflow is captured in an old plastic bin for dilution and is then applied to my garden. Along the gas line, a 'T' piece to a pressure release valve consisting of a bottle full of water into which a few cm of pipe gives you an added guarantee that you won't damage the airbed if too much gas happens. The cast iron burner can be hooked up to the half inch poly pipe gas supply without any modifications. If you happen to have an old camping stove that used the disposable gas bottles you will need to remove the plumbing and the high pressure jet valve before connecting the low pressure methane gas pipe. A bit of work required, but you can find old broken or discarded ones for free quite easily. All up, it cost me around $100 to build, and can be done in just one day. Give it a try. Sorry, I am unable to manipulate the images below as my IT skills are minimal.