The Origin of the Expression “Piss Like a Racehorse”

Race horses are commonly put on a drug called Lasix which is a diuretic which also helps to keep lungs from bleeding during the stresses of a race. Being a diuretic, it also causes the animal to Urinate much more frequently than normal, which also causes a temporary weight loss, beneficial to racing.

Always been curious why people use the expression, now I know.