I'd guess at putting a washing-up bowl under the rad and draining it that way... but you wount be able to pump the water round and out the system very well liek that. you're probally better letting it drain under gravity. and leave a washing up bown under the back end. it'll take a lot of fiddling, but if you're careful, you can usually tilt and move the system about so the majority of the water drains out like this...
Then, to flush the system, stick a pipe into a bottle/jug of de-ionised/distilled water or cleaning fluid of your choice and let it pump around for about an hour.
Refill in much the same way and off you go!
This is just my guess, looking at those pic's of yours. best just to look at which bits it would be easiest to collect the coolant from.
good luck!
MB4