which is the return line?

 

I can't recall which is the return line but know it is the cool, vice hot, line. Do the ol touch check with calibrated finger, with gloves on.
When installing new flat pan filter, keep it perfectly level and wiggle it gently while you push it in. It should be flush to the trans body when you replace the mounting screw. You do not want it cocked at all as this filter plugs directly into the tranny pump. You will get a caution light if improperly installed. I rec that you just do a pan drop and replace the 6 quarts vice full system flush. The two filter system works great and does good job of keeping the fluid clean. I did a full system flush (all 17 quarts) the first time. I drained the converter into clear containers and they stayed in my garage a week before being recycled. There was not a single speck of metal in the converter fluid. The tranny pan had a lot of metal fuzz in it though.