I've been searching for the human urinal scene, but I've never been able to find it. Where is it located and how can I make it happen?
If you mean what I think you do, you have to complete the short questline involving Dale in the barracks (The Sting and Death and Taxes). If you can give potions to Dale in the barracks, then you’ve already completed this part.
Go to the backstreets while you’re very dirty and you’ll have the option to talk to a woman, and doing so starts the request The Urinal, which unlocks the activity on completion.