Honestly I would probably avoid it in plain AutoCAD since you have limited editing ability after the pipes are modeled. I would stick with isometrics which you can accomplish by setting your snap from rectangular to iso. But since you asked...
I think using sweeps would work best. Basically you draw a polyline to represent the path, fillet your corners to have the correct radius for the size pipe you are using. After that you basically draw a profile (circle in this case) to sweep along the path. Look up "sweep" in help if you need a little help with the command.
It's been a while since I did this, but I believe in AutoCAD it is refered to as "extruding along a path." It's not too difficult, but it does take some getting used to. You may also have to look into the SUBTRACT method for removing material.
You would be better off purchasing a third party program to work inside Autocad. There are several programs avaialble. Mech-Q from Asvic Software seems to work well at a reasonable price.
Mech-Q is fine for what you need. But if you are OK with AutoCAD, you have all explained in Help. Also, look for some LISP files (3Dpipe) on Internet.
Good luck.
