Literal translation
to change the water for the olives
Meaning
to relieve oneself
Explanation
To pee, said of a man. The olives stand for the testicles, a common image in Provençal where fruit is used to evoke intimate parts discreetly. Real olives, for their part, only become edible after a long soak in brine whose water gets changed regularly, turning yellow with use, hence the image, considered elegant rather than vulgar.