leave a piss
Very similar to the phrase, "leave a shit" (popularised by the late great comedian George Carlin but with a different bodily waste product.
{Husoos}: Man I've got to take a piss!
{Horhay}: Hey Husoos! You can have that piss in the unflushed urinal over there; I'm going to leave a piss in this one.
{Husoos}: You a funny man Horhay!
{Horhay}: Hey Husoos! You can have that piss in the unflushed urinal over there; I'm going to leave a piss in this one.
{Husoos}: You a funny man Horhay!
Leave a piss
To urinate. Taken from "hey man im going to go take a piss." Noone actually takes it, they leave it.
"Hey man im going to go leave a piss"