I worked fast food as a teen in the early 70’s. It’s all about the management. Good managers have clean places. Bad mangers do not......................
My little brother used to work at a Long John Silvers.
He could not even wash his work clothes with other laundry; they were so greasy.
He confirmed that yes, they fry fish, chicken, fries, etc. all in the same grease. Which is why it is hard to tell the difference between their fish and/or chicken.