There is one thing to keep in mind when creating a design model - constructibility. For the particular issue here the type of connectors commercially available on the market needs to be considered. These vary depending on the pipe material. The materials obviously vary depending on the system type. You can still ignore this and just model the design intent and leave it up to the contractor to construct the pipe run as he is able, but in my opinion that is the less desirable option. Even if in this instance you were to model welded pipe connectors (where the end of the pipe sections and fittings can be cut to any angle desired, this makes the install way more expensive than using out of the box fittings only. The best choice for a one or two degree angle shift is grooved end connectors, which can be intentionally misaligned. Regardless of what you model the contractor is going to try and rearrange the system for the lowest possible legal cost install.

(For visual representation) If you've created a family that can handle the 2° angle, then your next best bet would be to change the 'Pipe Connector Tolerance' to the 'Value' of 1°, under Manage>MEP Setting>Mechanical Settings>Pipe Settings. Though i have not tested this myself, so good luck.

FYI - i was able to do the test successfully with a 3° elbow after changing the Pipe connector Tolerance, though it wasn't straight forward. First i changed the Pipe Type Properties, Fittings, Elbow to my 3 Degree Elbow from the Generic Elbow to override the auto solutions. Then i had to first draw the pipe on a 5 degree angle. Lastly i grabbed the end connector and pulled down the pipe to 3 degrees, which seemed to have worked. Hopefully you'll find a better approach.

Having no luck replicating this trick. Trying to get a 1:40 fall on a pipe and revit won't allow it. Any ideas?