Was this fast food place a sandwich shop per chance? I have seen the sub shops and you have to find the bathroom, because it is located somewhere inside the convenience store.
The Golden Arches (I shopped) has no bathroom because it is inside a W-World store, so I go inside the W-World store and notate on that restroom..just in case.
Do everything you can to find that bathroom!
ASK an employee if there is a bathroom ANYWHERE on the property.You can only report NO if it's out of order (happened to me twice) or being used longer than 15 minutes, in which I still wait....