You define a slope by specifying the gravity plane, the start point, the direction of the slope, and the slope value. The slope becomes a property of the route segment.
If one end of the pipe route is fixed, then vertical segments of the route are shortened or lengthened to accommodate the sloped pipe segment. If the other end of the pipe route is not fixed, then the entire pipe route, including the fittings, are adjusted to move up or down.