Impossible to change the rear differential fluid on the 2002 Volvo XC.
No drain plug. Factory "fill for life". No space inside the differential housing to fit a hose to siphon out the fluid. You can't feed a hose, even a small one, down inside the housing.
So, here's what I have had to do:
Cut a 2 foot piece of Mercedes hard vacuum line (4mm)
Connect to Mityvac reservoir with adapters
Drive the car to warm up the fluid (very important)
Put car up on ramps and while still warm, remove fill plug.
Slide line in past internal components to reach bottom of differential
Suck out old fluid.
It takes at least 10 minutes due to the small size of the line, but no other hose fits. They're all too big. If you don't warm up the fluid, it takes half an hour.
Refill with your choice of quality fluid.