You can do slope through multi point fill.  Start the command, pick your starting elevation (or click your start point if you have a placeholder there), click ok in the dialog.  then type e or click elevation in the command line, click work to fall, input your slope.  As  you are running, you can select what elbow you want where you want to put it, just click the correct elbow when you want to input it.  Or to make it easier, draw it all with one type of elbow, and go back and revdesign the sections you want to put in different elbows, excluding the unwanted ones from the pallet.