Sorry I missed this thread!!
Yes, as quoted above, I do mine by routing the hose to a bucket. Route both hoses if you don't know which is the pressure one. As was said before, the return line isn't suction, so it won't suck from a bucket.
First, a minor point. If making your cuts for the first time, try to tap the return line to the trans from the radiator. That way, the cooler and more lines get flushed as well. Otherwise, most of the lines and the cooler have old stuff in them when done, although you could blow it out with air into the pan as part of the process, but doing it this way is easier.
As you run it in P or N, it will start out at a full flow. Observe fluid color, preferably with some light behind the stream so you can judge transparency and color. Have someone start the car while you do the work with the lines. After a minute or so, the flow drops down a bit, but it's still a flow. After another short while (30 secs maybe) it will rapidly slow down, then start to spit air. I give a hand signal to the one in the car to kill it.
I usually kill it just before it spits air, but have done it after too with no ill effects. At this point, everything in the trans is still wet and lubed, but it is essentially as empty as can be. I then refill through the filler tube. I judge how much came out, then add it plus a little. I think at this point in most transmissions, all that remains is in the converter, and check valves keep it from coming back. The flow is: pan to servos and valves in the body to converter to cooler to pan. So, when you add through the filler, the old is separate from the new.
Anyway, have it started again and do it again. Near the end of this time, the fluid will suddenly look new as it comes out. I usually measure the first time on a car, both because it has the dirtiest fluid it'll have at that point and it's easiest to see the diff. It's always worked out to the rated capacity with converter - a full change. I'll let a couple more qts through for grins.
Now, when it stops, you just have the body to fill as the converter has new in it by now. Since everything is bathed in fluid in there, at no point does it ever truly 'run dry' in a damaging way. If you were to drop the pan, everything would be dripping wet.
It only gets tough if you change it when it still looks good (like you're supposed to
. But, with a good eye, you can always tell used from new as it comes out...
-Skip
