Update #2

We have acquired the manure from a local farm, and have built the 1st generator. We have about 30L of manure, more or less. We used about 6-8L of manure, and filled it close to the top with water. We needed a smaller balloon, but we just folded down the top of the old to lessen the space where the gas could collect. We now have to wait around a week or so for the maximum amount of gas to collect. It is  averaging at about 40 degrees outside, so it might affect how much gas will collect.