Transmission fluid change

I would like to change the fillter and the fluid in the pan on my 2000 Towncar. It is a 4R70W transmission. I have changed fluids and filters on other cars in the past, but not in this Lincoln. The pan has a low area that I don't understand. It is sort of a semi-circle about 3/4" wide. This area hangs down 1" or so.
I don't want any supprises after removing the pan. I would appreciate any advice someone could offer on this project!

You won't have any supprises, except that the pan gasket is REUSEABLE so don't throw it away, or use the POS cork thing you'll get with a new filter.

Here's how we do this: www.crownvic.net/tech/transservice.htm