It's interesting, I actually do think there is value in regionalizing media to an extent, primarily low-level word change between dialects. For example, changing "Go throw the wellies in the boot of the car parked on the pavement before we get petrol" to "Go throw the rainboots in the trunk of the car parked on the sidewalk before we get gas" for an American audience. Higher-level changes are less justifiable, like the potential of changing landmarks, etc.

That being said, "disused lavatory" is reasonable to change, although "unused lavatory" is entirely the wrong way to do it! That translation both changes the meaning of the phrase and doesn't even get rid of the obvious Britishism. I would have gone for "derelict bathroom" maybe? Maybe "dilapidated"?