What Ham said.
I pull out the bay res, open, flip it 180 in a bowl and get as much out like that.
Then I always stretch the pump out of the case, put in in a bowl, twist until a barb comes loose and let it drain.
Tip the case back/forward and the water from the rad comes out.
I just noticed the crap algae killing stuff hasn't worked. My loop has developed algae in the res, pump, and cpu block. I can't see in the rad but I bet it's in there too. I just want to get all my parts in and that damn case polished so I can clean everything up and move into my new case.