Having Read every one of the 11 pages on this post my thoughts are that its the work of some kind of nutter/fetishist. cab drivers relieving themselves into plastic bottles, keeping them and then dumping them en-masse, sometimes in weird formations just sounds too much hassle. After all, lets be honest, all a man needs to do is jump out his car, unzip his trousers, wee against a tree or a wall and jump back in the car again. The thought of someone sat in their car, aiming into a plastic bottle closing the lid then storing it until he's filled a few more bottles and dumping the lot in full view just doesn't make sense. I think someone gets some kind of weird kick doing this,like a peculiar OCD thing. perhaps they think its warding off evil spirits, or some kind of witchcraft ritual.