As above , does anyone know the best way to clean a grimy header tank. I've tried degreaser,detergent,bleach, even put it in the dishwasher(swmbo was well chuffed!) but still grubby. the only thing i can think of is a f@&king hammer!
Other ideas anyone???

If it's dirty inside, try a handfull of sharp sand with whatever cleaning fluid you use and give it a good shake

couple of marbles or small pebbles and and a dam good shake!!!