Civil 3d doesnt have the capability to draw vertical curved pipes, the only way u can do that is to split it in short straight segments and gradually change grade for each segment to make it look like its a vertical curve. I havent tried for myself but there may be a chance that u can manage that by doing a vertically curved alignment by adjusting the curve in a profile and then create a feature line from this alignement. Then u give the feature line PI:s with about 1 m distance and create your pipe from this result.
But im just guessing. Hope someone else can give som clarity to this!