Connection device for connecting a main pipe, provided with a connection bore, to a lateral pipe, • having a first end which is introducible into the main pipe through the connection bore, wherein, in the region of its first end, the connection device has a radially outwardly extending collar which is placeable from the inside against the main pipe, • having a second end which is connectable to the lateral pipe, wherein, in the region of its second end, the connection device has a connection section which is configured to be connectable to the lateral pipe, • having a main body which is in the form of a pipe section, • having an elastic seal on the collar that extends from the collar in the direction of the second end, • having a spacer ring which surrounds the main body outside the main pipe, wherein the spacer ring has, facing in the direction of the first end, a flange surface extending in an undulating manner and following the outer side of the main pipe and has, facing in the direction of the second end, a pressure surface extending transversely to the main body, and wherein the spacer ring is shaped in such a way that, between the spacer ring, at one side, and the main body and the main pipe, at the other side, a receiving space fillable with a flowable sealant is created, which receiving space is adjacent to the main body and the main pipe, and wherein an outer seal is arranged on the side of the flange surface facing towards the first end and delimits the receiving space, • and having a clamping ring, wherein the clamping ring surrounds the main body and is screwable to the latter and has, facing in the direction of the first end, a clamping surface placeable against the pressure surface of the spacer ring, characterized in that the seal has an encircling front sealing lip which extends outwards substantially in the radial direction, and in that the front sealing lip delimits the receiving space, creating a first part-space which is adjacent to the spacer ring, and in that the spacer ring has an injection channel which opens out into the first part-space. • having a first end which is introducible into the main pipe through the connection bore, wherein, in the region of its first end, the connection device has a radially outwardly extending collar which is placeable from the inside against the main pipe, • having a second end which is connectable to the lateral pipe, wherein, in the region of its second end, the connection device has a connection section which is configured to be connectable to the lateral pipe, • having a main body which is in the form of a pipe section, • having an elastic seal on the collar that extends from the collar in the direction of the second end, • having a spacer ring which surrounds the main body outside the main pipe, wherein the spacer ring has, facing in the direction of the first end, a flange surface extending in an undulating manner and following the outer side of the main pipe and has, facing in the direction of the second end, a pressure surface extending transversely to the main body, and wherein the spacer ring is shaped in such a way that, between the spacer ring, at one side, and the main body and the main pipe, at the other side, a receiving space fillable with a flowable sealant is created, which receiving space is adjacent to the main body and the main pipe, and wherein an outer seal is arranged on the side of the flange surface facing towards the first end and delimits the receiving space, wherein the spacer ring has, facing in the direction of the first end, a flange surface extending in an undulating manner and following the outer side of the main pipe and has, facing in the direction of the second end, a pressure surface extending transversely to the main body, and wherein the spacer ring is shaped in such a way that, between the spacer ring, at one side, and the main body and the main pipe, at the other side, a receiving space fillable with a flowable sealant is created, which receiving space is adjacent to the main body and the main pipe, and wherein an outer seal is arranged on the side of the flange surface facing towards the first end and delimits the receiving space, • and having a clamping ring, wherein the clamping ring surrounds the main body and is screwable to the latter and has, facing in the direction of the first end, a clamping surface placeable against the pressure surface of the spacer ring, characterized in that the seal has an encircling front sealing lip which extends outwards substantially in the radial direction, and in that the front sealing lip delimits the receiving space, creating a first part-space which is adjacent to the spacer ring, and in that the spacer ring has an injection channel which opens out into the first part-space. wherein the clamping ring surrounds the main body and is screwable to the latter and has, facing in the direction of the first end, a clamping surface placeable against the pressure surface of the spacer ring, characterized in that the seal has an encircling front sealing lip which extends outwards substantially in the radial direction, and in that the front sealing lip delimits the receiving space, creating a first part-space which is adjacent to the spacer ring, and in that the spacer ring has an injection channel which opens out into the first part-space.