NOVELTY - Biogas plant-fermenter tank comprises a service device having a gas-tight closable-, cover-side service opening that is closable by a cover device (15), through which a height adjustable Aqua-lung (44), preferably a submersible stirrer or a submersible pump is guided on a guide pole (17). The guide pole is mounted in a bearing point (18) of the service device, and is rotatable and/or pivotable using a bearing shaft (19). The bearing shaft is coupled for rotating or pivoting the guide pole by a guide pole pivoting device, which is arranged outside the fermenter tank.    USE - Used as biogas plant-fermenter tank.    ADVANTAGE - The biogas plant-fermenter tank: ensures that the pivoting of a guide pole and the height adjustment of a submersible device on a component can be carried out in simple and compact manner; and can be operated in a simple manner without causing the release of gas from the fermenter.    DETAILED DESCRIPTION - Biogas plant-fermenter tank comprises a service device having a gas-tight closable-, cover-side service opening that is closable by a cover device (15), through which a height adjustable Aqua-lung (44), preferably a submersible stirrer or a submersible pump is guided on a guide pole (17). The guide pole is mounted in a bearing point (18) of the service device, and is rotatable and/or pivotable using a bearing shaft (19). The bearing shaft is coupled for rotating or pivoting the guide pole by a guide pole pivoting device, which is arranged outside the fermenter tank. The Aqua-lung is coupled with an Aqua-lung-height adjustment device arranged outside the fermenter tank. The Aqua-lung-height adjustment device has a drive shaft, which is guided with the bearing shaft of the guide pole-pivoting device into a hollow shaft assembly by the bearing in the fermenter tank-interior space through the service device. The drive shaft in the fermenter tank-interior space interacts directly or indirectly with an adjusting element, by which the height of the Aqua-lung is adjusted at the guide pole. An INDEPENDENT CLAIM is also included for service device for the biogas plant-fermenter tank, comprising: a gas-tight closable service opening, which is closable by a flat- and/or plate-shaped cover, located in an accessible pedestal plate, and from which a shaft-like gaseous apron enclosing the annular service opening, in the assembled state of the pedestal plate, protrudes downwardly into a fermenter tank-interior space; and an Aqua-lung, which is guided in a height-adjustable manner into a bearing point of a guide pole, in which the pedestal plate adjacent to the service opening, is arranged in a pedestal plate region, preferably arranged in an edge region and/or within the gas apron adjacent- and/or directly associated to the service opening.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic cross section through an edge side portion of a biogas plant-fermenter tank with a roof sheet.    Cover device (15)    Guide pole (17)    Bearing point (18)    Bearing shaft (19)    Aqua-lung (44)