In Civil 3D, when working with gravity pipes, it is only possible to establish downstream slopes. That is, from a point of known coordinates and elevation, the slopes are established downstream. The reverse possibility, starting from a low point and establishing upstream slopes, does not seem to be available.
In pressure pipelines, both options are available.
Kindly requesting to consider incorporating the option of establishing upstream slopes in gravity pipelines. This request has been submitted by some users.