The Tube Diner, Paintworks
bath rd, Paintworks, bs4 3eh, bristol, avon
100% positive
Directions: Drive/walk into the Paintworks entrance and it's on your right past some bin sheds, two large silver air streams, the one on the left is the kitchen/ordering counter, you can just ask Charlie the man who works there for a key to the bathroom which he will direct you to.
Comments: you might want to grab a water (if you're looking for the cheapest thing) it's actually lovely-and accessible if you sit outside.