Cored manhole: the cylinder of the manhole of the general type tank and the tank wall is the one that goes through the wall of the tank relative to the floating roof tank. This manhole is not conducive to the buoyancy and seal of the floating plate. The core manhole is a core plate that is equal to the curved wall in the manhole cover, and it is flush with the tank wall. In order to facilitate the opening and closing, there are also rotating arms and lifting lugs on the joint barrel of the hole. The manhole cover is still not out of the tank. The inner floating roof tank manhole is usually set at least two: one is about 700mm from the bottom plate of the tank, and is used to clean the tank and the maintenance personnel. A distance of about 2400mm from the bottom of the tank, for the operator to board the float.