I don't think there is a drain plug.
Get two or three drain pans, plastic dish pans from the dollar store work ok because you can put them next to each other and they have straight sides. Any largepan is OK, the larger the better, if you look at the trans pan you'll see how much area you want covered. A cheap tarp would work to catch drips and spills if you only have one pan.
You remove the pan bolts from on side totally, then loosen the ones left as you work towards the other end. You want the pan to slowly drop down and drain from the side you removed first. As it empties you remove the bolts to let it drop more. Careful when you pull the last one as there is still some fluid left.
Check the pan for how much metal is in it. That's indicator of wear. Replace the filter making sure the rubber seal comes out (they tend to stick). If you have to pry be careful not to scratch the opening too much or you'll have an internal leak. Clean the pan and reinstall. I'm including an interesting link to a procedure on flushing a Taurus trans. It is well written. A few details may be different but the basics are the same. Flushing like this gets the fluid out of the torque converter. Otherwise you are leaving about half of the old fluid in.
Thanks to Don Rimdzius (via Jim Heaton) for this ATX Fluid change procedure:
The '96 Ford service manual recommends the following procedure to change the transmission fluid. This will get out almost all the old fluid including the torque converter in one shot:
1) disconnect the lower transaxle fluid cooler line.
2) start engine, keep at idle, and fluid will drain from the open cooler line.
3) stop engine immediately when steady stream stops flowing (2 to 3 quarts will drain)
4) With engine stopped, add 10 quarts of new fluid to transmission. Don't worry, it won't overflow or damage anything.
5) start engine again and fluid will again drain from open cooler line.
6) stop engine when steady stream stops flowing (10 quarts will drain)
7) reconnect trans cooler line.
8) add 2 quarts of new fluid to transmission
9) check fluid level under normal operating temp and add in 1/2 pint increments until full.
Apparently, the oil is some what stratified as it drains removing old oil first. I've used this procedure on all 3 of my Fords ( '89 Taurus with AXOD, 95 Windstar with AX4S) with excellent results. I only use Mobil synthetic trans fluid and feel the superior temp rating is great insurance against premature trans failure. My '89 has Ford's engine mount wrenching 3.8L with 230 ft. lbs. torque and My Windstar pulls a trailer. The Synthetic fluid will cost about $75 for this change.