A couple ways I know of:
-Make a series of curves using the straight and arc tools, moving them up and down when needed, make a circle or half-circle (along with the offset tool) at the start, and use the 'follow me' tool to trace the path.
-Make the waterslide path in No Limits 1, put tunnels over it, and then import it into Construction Kit, save only the tunnels, and export, and if needed, import into SketchUp if you want any half-pipe segments or independently colored segments.
Both ways have their own sets of challenges. The first way I mentioned is easier to get a custom width but the latter is easier to make the layout and LOD's.