Suction gun sucks when it comes to gear oil. Biggest POS I have ever used. Had a 5ver of Red Tacky which I used in the diffs and t-case and it was a pain to fill the gun.

I would drill a hole on the side and either weld on a bung with a plug or use a self tapping oil pan plug with 1 of those washers that have a rubber seal. After all you'll probably have to drain it again.