How long do mammals urinate for?
Interestingly, mammals empty their bladders on average for 21 seconds (standard deviation 13 seconds), despite a difference in bladder volume from 0.15 ml (mouse bladder) and 300 ml (human) to 18 L (elephant) and 300 L (blue whale). Oh yes, the blue whale heart is 200 kg.
This is called the Law of Urination.
It occurs because urethral length increases in proportion to the size of the animal, which amplifies gravitational force and flow rate.
In other words, the urethra has evolved as a flow-enhancing device, enabling the urinary system to be scaled up without compromising its function.
MyHSN has a related article on what does the bladder do
