In the promotional picture for the series it shows a shirtless Oliver. The scars from his time on the island are visible, but there is no tattoo. During the series Oliver has a tattoo on his chest, a tattoo that plays an important role in at least one episode (1x03 "Lone Gunmen") and has been visible in every other episode.
None of the prisons have toilets. Even the worst super-villain needs a sanitary stop every now and then.