The invention involves a device and a process which can be employed for sealing building branch lines (3b) leading from a building or a collecting manhole directly to a sewer main (4) using a relining process in which liners (1) made of self-hardening/self-curing sealant are used. In the process according to the invention, a pipe repairing machine (6) is employed which features a rope guiding device (10) at its front end (14), said rope guiding device (10) being comprised of a roller mount (15) to which a deflection pulley (5) and a retaining roller (16) are affixed. The pipe repairing machine (6) into whose rope guiding device (10) the rope (7) to which the liner (1) is attached is threaded is positioned inside the sewer main (4) at the building branch line junction (2) in such a manner that the rope (7) does not come into contact with the building branch line edge (9) facing the pipe repairing machine (6) when taut. While the rope (7) is being pulled through the building branch line (3b), a support foot (11) with a brake block (12) ensures that the pipe repairing machine (6) does not shift.