A liquid lock is for a fermentation receptacle for production of biogas, the liquid lock being provided as an annular liquid filled vessel encircling an upper portion of the receptacle wall(s), an inner portion of a fabric being fastened to the receptacle, an edge portion of a receptacle cover encircling the inner fabric portion, and an outer fabric portion extending upwardly along the edge portion and fastened to the receptacle cover, and conduit connections are provided between an internal space in the receptacle and the liquid lock.
