I've used a little drill pump like this one to fill my W56 tranny and it worked well. I bought mine a Menards for about $4 if I remember correctly and I got some poly tubing that fits tightly into the in/out holes on the pump.

http://www.hardwarestore.com/pop-print/larger-image.aspx?prodNo=2037


1990 Truck 4X4 5sp 22re