A method for joining at least two plastic elements in a liquid- and/or gastight manner, whereby an edge of a first plastic element is at least partially placed in an opening of a second plastic element, the edge of the first plastic element being folded over an edge of the opening of the second plastic element under plastic deformation, using a pressure device. The edge of the first plastic element is pressed against a curved butting face of a pressure body placed in the second plastic element at the opening thereof and the edge of the first plastic element along the butting face is pushed radially outwardly and over the edge of the opening of the second plastic element. The edges of both plastic elements are pressed together by exerting pressure on both sides of the edges. Alternatively, use is made of a sealing ring at least partially between the edges.