OMG - I do this all the time! My two fav techniques are vinegar in water and boil it on the stove to losen it and then scrub with scourer. Or I use a lemon cut up and boiled. Both work brilliantly for getting rid of tough marks (also use the lemon one to clean my microwave and oven). Honeslty, vinegar leaves my sink and pots shining!

HTH

MG

P.S. Lulu - I'm going to try your one!