Solar C³ities is an international platform with the intention of providing an open-source virtual Hackspace for "Biogas Innoventors and Practitioners" and training for all those researching, developing and deploying sustainable solutions for flourishing societies.
Read more about Solar C³ITIES and our Team
Gas will always float to the surface of a liquid, so even if your tank is full to the top; as gas is formed, it will bubble up to the highest point and escape from the outlet hole. As for drainage, the outlet channel should be lower than the input channel, if thats the case, then as you feed the digestor, any extra liquid will flow out from the shortest pipe first. I would only recommend keeping your gas outlet closed during feeding to prevent any sludgy material going up the gas outlet tube and creating clogging.