Method in which the following operations are carried out: a) digging an exploration hole (8) in order to open up a main pipeline (2) which has an upper edge (10) which extends at an upper level (12) which is substantially constant relative to the ground (6), b) using a branch connection (14) which has a support surface (16) and a shaft (18) to which the branch pipe is connected, c) positioning the support surface (16) of the branch connection (14) against the main pipeline (2) so that the shaft (18) is below the upper level (12) of the main pipeline (2), d) fixing the branch connection (14) to the main pipeline (2), e) placing the branch pipe and the main pipeline (2) in communication, f) refilling the exploration hole (8), whilst keeping the branch pipe below the upper level (12) of the main pipeline (2).