i've used sugar soap pretty effectively in the past, you can buy it in wilkinsons... it's used when decorating to clean walls down before painting and stuff, (well that's what my parents used it for) be warned though, if the paint on your walls is not very thick (likely if it's a student flat and they just did it on the cheap), then it comes off if you scrub too hard... so just kinda, dab at it with a cloth (wear gloves as the mix dries your skin out really quickly... it says that on the tin, it's not lying). Another problem you might have is if the walls haven't been properly cleaned in ages... the dirt from that can come out, as happened to me and I ended up with black streaks down the wall, but you can just wipe that off. It might work on the printer ink too, not sure though.