When, after drinking a significant amount of liquid -e.g. coffee or beer- over the course of a few hours, you anally penetrate a female's asshole with your erect penis and proceed to urinate until your bladder has been emptied.
If the amount of urine expelled into the female's colon is any less than one standard pint, the act is then referred to as a Mexican Leak
Guy 1: "My wife is a fat whore who won't stop eating cheese. She's constipated for the 5th time this month, that disgusting bitch."
Guy 2: "Just buy her some Mexican food and it ought to clear her right out. Better yet, just give her a Mexican enema."