Every lunchtime, at about 1.10pm, a strange white foam used to emerge from the bottom of the pipes. Children used to play with it - run around the playground with it on their faces in winter pretending to be Father Christmas, or in summer, an ice-cream to fun and fool your friends with.
I now realise that this was the cooks emptying the sinks of all the greasy, fatty, food-encrusted gunk. This, added to a dash of Fairy Liquid, would cause giant clouds of this foul-stinking dirt. Everyone from Hillbrook School will probably get cancer from this by the age of 40.