Random guessing here* First, we can assume that a T-Rex will be a huge amount at a time. Probably a few liters. read more
Well to quote Eric, "you don't want to know". My theory is that T-Rex, like other predators would pee to mark its territory. All Eric had to do was pee in the Rex's territory and leave the bottle snugly embedded in the ground where the Rex's urine would simply run into it as the Rex peed. He may even have dug a channel to ensure run off. read more