Question 1: Can I use petrol as a chain cleaner in my whirring-brush plasctic box before drying and lubing?
It might dissolve the box.
Question 2: If not petrol, what?
Why does it need cleaning? By cleaning the grit off the visible, outer parts of the chain, very fine particles become suspended and get drawn into the pins, which wears them, accelerating "stretch". Surely it's best to leave the dirt where it is? At most, wipe the outer sides of the plates with a rag.
Just lightly touching each roller with oil from a small brush, the oil will get where it needs to by capillary action, without disturbing and drawing in existing dirt and leaves minimal residue for more dirt to stick.