Thanks all for your ideas and suggestions. I was able to finish the job
this afternoon. I ended up just using brute force to twist the two
45-degree angled fittings to where they made the complex angle turn I needed
etc. What helped was that I put a piece of 3-inch PVC in the bottom
45-degree coupling and used that for leverage to turn that one.

Jay-T wrote:
I am pre-fitting some PVC fitting for a 3-inch sewer drain line
coming down from a first-floor toilet. Where the drain comes through
the basement ceiling from the toilet, there are two 45-degree 3-inch
fittings -- one is the toilet flange itself which is a 45-degree
fitting and the other is a 45-degree elbow. The place where they
come through the ceiling is hard to access.

What I would like to be able to do is put the two PVC fittings
together and then be able to easily rotate both so I can get the
correct angle I need to continue the run. The problem is that when I
put the two fittings together, they are next to impossible to rotate
while in place. I need the fittings to be able to rotate one inside
the other to get the correct line-up.
Has anyone ever tried lubricating PVC fittings first just to get the
fittings lined up correctly, then marking them for the correct
line-up, and then remove the lubricant and glue the fittings
together? Does anyone know what kind of lubricant might work for
this? So far, I have just tried dish soap, but that doesn't work --
the parts just stick together as usual and do not turn easily. Any
suggestions on what to use?