Thanks to all for these replies. As I understand it now, water goes in each of the wells, the pink'un sits on the divider, the sponge gets saturated in one well and rinsed in the other, right? Armed with this new insight, I'll chalk up the top & tail as a 7 pound "learning experience". It's astonishing to think somebody probably got rich for inventing this. I'll just hijack a laundry basket and fill it with water...
If anybody wants a brand-new top & tail, FREE, except for postage, here's your chance!