If you are a black cab driver, constantly delivering passengers or roaming around London in search of a fare, what do you do when you need to pee.
Note the wide neck of the fabric conditioner bottle, above. Out of my office window this morning i watched a black cab draw up to the kerb, pull out a fabric conditioner bottle, unzip, and relieve himself. He then screwed the top back on and drove off. So now you know.