Connection assembly for connecting a main pipe to a side pipe, which main pipe is provided with a radial hole, • having a first end that can be inserted through the radial hole into the main pipe, where the connection assembly incorporates in the area of its first end a coupling piece that can be placed against the main pipe from inside and extends radially outwards, • having a second end that can be attached to the side pipe, where the connection assembly incorporates in the area of its second end a connection section that is configured for attachment to the side pipe, • and where the coupling piece is provided with an elastic seal that extends from the coupling piece in the direction of the second end, • and having a main member configured as a pipe section, • and having a spacer ring that during use fits around the main member outside the main pipe and that incorporates a flange face extending corrugatedly towards the first end and following the outside of the main pipe, and a compression face extending across the main member and oriented towards the second end, • and having a locking ring that fits around the main member and can be bolted to the main member, and which incorporates a locking face that is oriented towards the second end and can be placed against a compression face of the spacer ring, where the spacer ring is formed so that a cavity that is adjacent to the main member and the main pipe and can be filled with a liquid sealing medium can be created between the spacer ring, on the one hand, and the main member and the main pipe, on the other, and where a soft seal delimiting the cavity is disposed on the side of the flange face that is oriented towards the first end, characterised in that • the seal that is fitted against the coupling piece incorporates a section that can be placed against the inner surface of the main pipe and that extends for at least 3 mm in the direction of the second end, and • the spacer ring incorporates two opposing holes (25, 26) that extend into the cavity and that are disposed in an axial direction of the main member at different distances from the first end. • having a first end that can be inserted through the radial hole into the main pipe, where the connection assembly incorporates in the area of its first end a coupling piece that can be placed against the main pipe from inside and extends radially outwards, • having a second end that can be attached to the side pipe, where the connection assembly incorporates in the area of its second end a connection section that is configured for attachment to the side pipe, • and where the coupling piece is provided with an elastic seal that extends from the coupling piece in the direction of the second end, • and having a main member configured as a pipe section, • and having a spacer ring that during use fits around the main member outside the main pipe and that incorporates a flange face extending corrugatedly towards the first end and following the outside of the main pipe, and a compression face extending across the main member and oriented towards the second end, • and having a locking ring that fits around the main member and can be bolted to the main member, and which incorporates a locking face that is oriented towards the second end and can be placed against a compression face of the spacer ring, where the spacer ring is formed so that a cavity that is adjacent to the main member and the main pipe and can be filled with a liquid sealing medium can be created between the spacer ring, on the one hand, and the main member and the main pipe, on the other, and where a soft seal delimiting the cavity is disposed on the side of the flange face that is oriented towards the first end, • the seal that is fitted against the coupling piece incorporates a section that can be placed against the inner surface of the main pipe and that extends for at least 3 mm in the direction of the second end, and • the spacer ring incorporates two opposing holes (25, 26) that extend into the cavity and that are disposed in an axial direction of the main member at different distances from the first end.