This sounds like a good exercise for getting proficient with Move and Rotate. I would set the insertion points for the pipe on the center line of the pipe and at one end. I would also add cross hairs on the ends of the fittings to provide snap to points for inserting the pipe components. You could add some temporary geometry to the pipes if needed but you should be able to get the Rotate tool to lock in to the desired direction and hold it with Shift.
Another option would be to create some faces at the various rotation angles to use to set the rotation.
And for an additional option, make square cross section proxies for your pipe components. Maybe make them 1 in. square. Set their component origins and axes to match the pipe components. Then you can position the square sections and replace them with the pipe components.
If you could share an example of what you’re doing, maybe I can give more specifics.