This ones pretty simple. Go do the Art Gallery job on any difficulty (If you want to get just the achievement, DS for more guards. If you want to finish the job then whatever difficulty your comfortable stealthing a job with.) I would recommend Six Sense at least Basic to see guards through the bathroom wall, a spycam in the Reception Area and Hall E so you can see them coming through walls and the Burglar perk deck for faster pagers. Dress for stealth (This is kinda obvious). Go straight to the right side of the building, sit in the bathroom and wait. When you see a guard come around the corner into the Reception Area from Hall E trigger the hand dryers so he comes in to check them. Drop the guard, Answer the pager, Bag the body and throw it in one of the stalls. Repeat.