I want to drain and fill the differential.

At the front of the differential is a plug with a square recess. Is this the fill plug and should oil be filled to the bottom of this hole? What is puzzling to me is that all the differentials I have encountered take oil to a level just above the bottom of the axle tubes, and therefore below the centre line of the differential. This plug is above the centre line, so the differential will be more than half full of oil if filled up to this plug.

There is another plug further up that has a hex recess, thus taking an allen key. What is this plug for?

I did not jack up the forklift, so I did not see the bottom of the differential. Feeling under the differential, there are two plugs located at the back and towards the bottom of the differential. These have hex heads on them, thus taking an ordinary wrench. Is one of these the drain plug?