monroews
commented
2 years ago I easily get confused by the various coordinate systems and generally end up trying to move in each of the 3 directions to see how the coordinate system of the mate connector is oriented. In this case check what happens if you move in the z direction.
The other possibility is that your sketch is constrained to components of the tank and thus those constraints don't change when you move the sketch plane.
Trying to figure out how to move the pipeline in the Y direction. The X works just fine, but when I try to move the mate connector in the Y direction it just shifts the underlying sketch without moving the actual pipeline.