Dreadsteel said...
drop some bleach in there, close the lid and open a window
An excellent and sensible suggestion of course :) as long as you do it immediately afterwards.
I tried everything known to mankind and the stain will NOT shift.
But for myself, since being diagnosed with UC, I have also developed a sensitivity to chemicals. All chemicals like bleach, shower cleaning agents, shower gel, hairspray, perfume, aftershave, deodorant, air freshener, perfumes in laundry powder, paint, petrol. So all this is now banned from our house.