Well, first rule of transmissions is, always remove the level plug before the drain plug. Because if you do it the other way round and the level plug won't come out - you're stuffed.
This axle is unusual in that most drain plugs are on the bottom pointing down, whereas this is one of the rear cover bolts.
Refill through the level hole and - quite right - when it dribbles out it's to level. Because the rear will be jacked up - unless you have a pit, you need to lower it to get a true level, before refitting the giant level plug (using an adjustable spanner).
