I recently replaced the fluid and filter in mine. Although this is interesting way to do it I used one of those pump up garden sprayers in which I added a shut off valve to the output hose. Fill the container with ATF, pump it up and open the valve

you may as well drop the pan and replace the filter while you’re at it.

I would also buy a new filler and drain plug. They’re cheap and you will thank me later. The drain plug was fine but the fill plug was slightly rounded and had a heckuva time breaking it loose

Jeff