Manhole is one of the most common equipment to get access inside the digester. The features of the manhole are: flexible design according to digester thickness and diameter as well as the easiness of installation and its steel material. Its gate is connected to the joint and opens inside ward. Therefore, it has a great pressure resistance to the pressure exerted from the inside materials of the digester. And it is ozone, UV, oil, methane and sludge proof.