Well the rad will help cool your pc if your using it to blow all the air out of the pc as it would suck it out of the case, thats what mine will do when i get around to doing the side panel

Plust almost everyone with on of these beasts puts there loops internally and there really isn't a huge difference in temps in having your rad internally imo.
Plenty of people have mounted it on the bottom with the holes cut in the bottom, if your worried about dust then get some dust filters to go on the front of your fans. Air flow isn't a problem either becuase of the case being off the ground on wheels.
As for the top mounting this is what most people do, only problem is if you have say 2 or more PCI cards as a PCI slot is blocked with it mounted up top, you also loose 2 5.25 bays. I personally mounted it at the bottom but sideways as i thought it would be coold to have the fans glowing out the side of me panel
As for purging/emptying the system I have a valve between my rad and pump (both at the bottom of the loop) so just open that to drain it.
EDIT: Oh forgot to say that worklog was my first time watercooling and my first time in modding a case!!!

Don't think i did to bad personally for a girl that is

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