gear oil sucks, but I cooked this up to help
 

Without a lift changing the gear oil in the three differentials is a pain in the butt. I've spent way too much time on my back/side/belly trying to pump thick oil out a bottle with a stupid little hand pump. Don't get me started as to why the damn feed tube ALWAYS falls off the bottom of the pump and winds up on the bottom of the oil jug.

I decided to figure out a better way.

One $10 one-gallon spray tank, a clamp, and a length of hose made life much easier. It still took quite some time to fill the diffs, and the fill plug on the center diff is still a pain, but my days of messing with that stupid little pump and tube that falls into the jug are over.

The white rag around the handle is there to hold the valve open.

Is it the most robust system? No. If I were doing this regularly I'd buy the proper pump but this worked well enough for my purposes.

I made one like that once. Watching paint dry was faster. Bought a pump for a 5 gallon pail and 5 gallons of gear lube. Soooooooo much easier and faster.
https://smile.amazon.com/Lumax-LX-13...8-5&th=1&psc=1

Yeah, it is slow, that is for sure. But I just set it up and go have a beer. Maybe pump some more air pressure while I wait every once in a while.

If I had a convenient place to store it, multiple trucks, and did it more than once every 12-18 months I'd upgrade to your solution which is far better. Five gallons of gear oil would last 3+ years for me.

For the tidy sum of $10 vs the $5-7 for one of the f'n plastic hand pumps then sell in the auto parts stores, it is not even close.