Never intended as a rule, it began when an 18th century Wordsmith cautioned against placing a preposition at the end of a sentence
when this will separate it from its verb by many words, as this makes the sentence awkward to read.
When most horses take a leak, it is a dramatic sight, with the stream typically about one-third to one-half an inch in diameter,
creating a veritable“river” of urine that seems to have impressed some Wordsmith sufficiently to coin the phrase,“piss like a(race)horse”-
today denoting a full human bladder that needs emptied yesterday.