Just use your hands to get it in and hand tighten it, then tighten it fully with a ring-ended spanner, same one you used to open it.
I did mine last Thurs, piece of ****, oil that came out was black & mingin' (did it just after the drive home from work so it was still warm to help pull more crap put), put in some nice fresh oil and all squaking noises gone! Not a peep to be heard. However I found the hardest part was refilling the diff.
Getting the fluid in I found was the easiest part. I used a squeezy bottle attached to 8" of plastic tubing and attached a bit of strong wire and bent the top of the tubing to an 90 dgree angle and in she went. As I said, with the fill plug I could just bout get it up the hole, but couldnt turn it making it impossible to screw in! It was imposssible to hold and screw due to the complete lack of room. Im going to invest in an off set ratchet spanner, that ill do it