How to grease an internal hub gear? Are there any online tutorials or can someone explain how to grease an internal hub gear?

I did a bit of searching but I only find people completely desassembling their hub gears. I am looking for a more practical day-to-day example.
Typically you will find a nipple on the hub that allows you to drain out the gear oil and then replace with new fresh oil which greases the gears. The placement and instructions for doing this depend largely on the type and brand.