You can simply remove one of the bolts (lowest one is best) that hold the differential in. If you look at the driver side axle where it meets the trans, it is surrounded by bolts, those are the ones I'm talking about. Jack the car up and down and all kinds of stuff to get it to drain.
I refilled mine with Syncromesh and I love it.
I realize this thread is old, but for info seekers Just note two things here:
1. Those bolts hold the ring gear bearing carrier or whatever it's called, so when you replace the bolt, torque it to the proper specs just to be safe.
2. Kind of a small hole for draining fluid - hence the recommendation to "jack the car up and down...etc..." - Just a theory, but maybe removing the fill plug will help so that air can follow behind the draining fluid. Also, you likely cant get all of the fluid out this was as it appears there are cavities lower in the differential and side cover areas that won't drain, also if you have metal particle or sediment, it will probably stay in the transmission down in those areas that didn't fully drain.
A tip for the side cover to prevent warping it from prying or pulling the next section of casting loose is to run a utility blade along the RTV bead to break it loose, then use a razor paint scraper to clean up both mating surfaces.
Oh, and the comment on A520's being junk is not at all true - Not everyone needs an A555 or A568, you know. In reverse, the A520 is basically an A555 with different gears. The main weaknesses of the A525 are in the case. Flexing in the case allowed internals to wear and break early. I believe the A520 had shifting improvements over the A525 as well, but maybe not as good as the A555. Unless you have a T-II+ or equivalent, the A520(Or 523 for you H-pattern cars) is a fine gearbox.