Working on your back with only one pair of hands that are covered in ATF discourages playing with cameras.
Nevertheless, Evin X took a pic of me doing this very job when I changed the pan filter and gave his transmission a full flush, but it was his job to start and stop the engine and only snapped a Jazz1 standard photograph. .
It's not rocket science, one line is flow from transmission to cooler and the other is return from cooler to transmission, whichever you take off will let ATF out.
The trick is catching the ATF in a bucket without it going up your sleeve.