Tinkle, tinkle, little star...

I just read that the first man to successfully pee on the moon and return safely to Earth was Buzz Aldrin. Buzz, AKA: the Lunar-leaker, says that while he may not have been the first man to walk on the moon, it is undisputed that he was the first to "water the horse" there. Be that as it may my question is this; where on the moon did he find a tree to pee behind?

Anyway... Humouroceros