All mammals great and small take about 21 seconds to pee:
[I]t’s a process driven by the way mammalian urinary systems evolved to eject fluids from the body in the quickest and most efficient way allowable by physics. To make this discovery, Patricia Yang and colleagues brought their high-speed camera to the Atlanta Zoo. They filmed male and female rats, dogs, goats, cows, and elephants taking a whiz. … This allowed them to create a mathematical model of urinary systems – a model showing that mammals take the same time to empty their bladders despite considerable differences in the size of their bladders – differences in volume than can range from 100 milliliters to 100 liters.
Jacob Aron has an in-depth explanation of Yang’s work, which takes into account gravity, viscosity, surface tension, and urethral anatomy. He concludes that the research may “inspire new designs for water towers.”
The Dish 