After finding out in a very messy way that the transmission cooler inlet is on the bottom in our 2002 Bonneville, I figured I'd share a couple thoughts on flushing the transmission. I was trying to flush it as I had done so before following these instructions
for a Crown Vic. The bottom line to the transmission cooler was rather difficult to get to so I started by removing the top line and hoping that it was the inlet. It wasn't, but it was impressive how forcefully the fluid sprayed out
All the transmission lines appear to be threaded 3/8" NPT - yes, SAE.
Likely due to lack of clearance, I couldn't get a pipe to screw in on the top bung of the cooler. After seeing the corrosion on the transmission end of that line (the one flowing from the cooler to the transmission), and not wanting to run out and get a 19mm line wrench, I opted to remove the sending line. This was the one in which the fitting pointed straight down. I screwed a 10" long pipe directly into that port, with the other end pointing into my drain pan. It screwed in very easily once the threads hooked, confirming that they're 3/8". If I had to do it again though I would just remove the other line connecting to the transmission and flush the cooler at the same time.
I contemplated draining the torque converter, but after removing the cover plate I couldn't see how there could be enough room to get to the drain plug if there was one, and I didn't pursue it any further.
My last tidbit is for removing the old seal for the transmission filter. That little thing is in there pretty tight. Already having my plumbing parts out, I found that a 1/2" NPT pipe is just the right tool for the job. Screw it into it and wiggle the sucker out.