Apart from the obvious meaning of urinating in the swimming pool, this term is also used to describe when someone is stealthily disturbing someone else's party or other gathering.
Spreading the rumour that there was something wrong with the drinks, Johnny was really peeing in the pool at Henry's place.
Nickname given to bales of marijuana thrown overboard or out of airplanes. Origin is reportedly from members of the US Coast Guard in the area of Southern Florida.