Cooking gas from compost and animal fecal wastes

Well, methane gas might kinda be really harmful for the atmosphere and the protective layers of the earth and global warming.
But what if , we could use all these gases without wasting a thing?
well, many farm based communities in third world countries actually use this technology of producing cooking gas and manure at the same time. The manure is organic which works great for all the organic freaks as well.
The procedure involves basically building a simple underground tank which is fitted with intlets and outlets and pressure gauge and and a gas outlet too.
The animal wastes are mixed with adequate water if any and let into this tank and as the wastes rot, methane rises to the top of the tank and then passes out through the top gas tube to the farmer's kitchen for cooking. Meanwhile the other outlet is for the sludge after all this gasesous emnation useful as manure for your farm or kitchen garden(organic farming) .
This cooking gas is so much better than the firewood fuel many backward farm based communities still use there.
If you have a small farm with animals, You might as well try this out .
Speaking of animal wastes, i am pretty sure, this same thing can be done with a human septic tank too. Though ofcourse, the output will be not so much as to do regualar cooking all the time.
Worth a try though.