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?