The way Jay described is exactly the same as sucking it with the pump, but a lot more messy. The torque converter still has the old oil no matter what, the only way to replace it is to take the gearbox off and drain the torque converter.
Jay my manual book says that after dropping the sump you suppose to replace the filter and the gasket, did you do that? The fill hole is the dipstick -) We lucky to have one, most of the Mercedes hasn't got one at all, nor the drain plug!
My manual says that the overall amount of ATF needed incl. Torque converter is 7.2 L. The way I replace it is suck everything off with the pump (around 4 L), put a new oil in (do it slowly), then I drive the car for about 2 weeks and do the same job again, this way 75% of the fluid will be changed. I've done it 3 times when I first bought the car.
I would highly recommend the FUCHS ATF oil, you will notice a massive difference in gear changes and better fuel economy after putting that oil in.
Fuchs TITAN ATF 4400 Automatic Transmission Fluid for Japanese cars
http://www.opieoils.co.uk/p-60163-f...tic-transmission-fluid-for-japanese-cars.aspx
There is another way of doing the job, but not the safest one - you can unplug the gearbox oil cooler pipes and drain the old fluid at the same time as filling a new one, for this the car has to be in D, but it's not safe as you have to provide constant feed for the gearbox, also it would consume quite a lot of new fluid, but it's 100% fluid replacement.
Did you know that our gearboxes can be tuned? Unfortunately nobody in the UK does it, but I was able to find a gearbox tuner in Russia, who claim that he can do faster gear changes and a stall start (when you will be able to build up the revs).
http://www.youtube.com/watch?v=0dsO2jDs61U