If the pipe IDs are the same you might be able to find a piece of pipe that fits inside both, where its OD gives you an 'interference fit'.
If the pipe section OD is slightly oversize you can spin it with an electric drill motor and slide sandpaper over its surface to take off a few thousandths.
Cooling the pipe section in the freezer and then allowing it to expand in place might also work if the thermal expansion doesn't split either pipe.
Epoxy can serve as waterproofing and, while uncured, a lubricant.
You probably want at least an inch of pipe overlap at each end but normally there should not be horizontal force, nor tensile force, on this splice. However, there may be some bending force as you have found out.
Interesting problem. Thanks for posting it.