I've been using a small hand operated pump for some time now to transfer fluids while working on my Mustang. I finally got tired of laying on my back pumping in transmission fluid, and made an electric pump to do the job.

Materials:
(Radio Shack or your local auto parts house)

small 12 volt electric fuel pump  $30
cigarette lighter extension cord  $6
on-off switch  $2
terminal lugs  $1
alligator clips  $2
clear hose  $3
scrap piece of wood or metal plate for mounting the pump $.20

1. Cut the socket end off the extension cord. leave about a foot of cord on the socket end. attach the alligator clips to the socket end wires, and put lugs on the plug end (optional, depends on how you intend to attach the cord to the pump).  This way you can clip the socket to the battery (or other 12 volt power source) if you don't have a cigarette lighter socket handy.

2. Assemble the parts to the pump. I used teflon tape to seal the threaded barbed pieces to the pump.  Mark all sides of the pump housing with an arrow indicating the fluid flow.  Put the hose on both ends of the pump. I cut the hose in two, making one piece longer than the other.

4. Wire the switch between the pump and the extension cord. Solder or use the terminal lugs. (lugs are easier to make field repairs if needed, so I used them). I recommend putting the switch close to the pump.

works just great. I put 3 quarts of GM Syncromesh fluid in my Tremec using this rig, and it's 75w fluid. I also use it on my rear diff.  I reverse the flow and stick the suction hose into the fill hole.  It will suck all but about 1/8 cup of fluid out of the center section.  Keeps the job real clean.