Ross,

I have had the same experience with the topsider. I also keep pumping with the unit gurgling away for about 10 minutes. I then let the car sit for about 30 minutes (just to make sure I get as much old oil as possible into the bottom of the pan, and then go back with the topsider and suck out anything that is left.
With the topsider or any method, changing hot and often (as Larry says) is essential for long engine life.

I keep the used oil in old 5 gallon paint containers (the plastic ones)
If you want something really big, get an empty 50 gallon oil drum (and also buy a wheeler to move it when it is full)
To lift it to a truck, well, eat 45 bowls of Wheaties in the morning.