Thanks Bderick I'm glad you said something now my luck I would have drained the tank pulled it out enough to get filter on then fill it back up turn the filter on go to put the lid on just to find out I now have to drain tank again just to pull it out another half inch lol.
I'd always leave at least an inch of space behind the filter. Your wall will get all grotty otherwise. Also, I'd move the tank, pump the filter on, then fill it. No worries about space then.