Ok. Thanks for all the replies.
What dilution do i need to use on this? I am thinking to reduce waste and as i have no bath i am goint to make a box of similat shape to the frame so that it fits neatly. Therefore the amount of acid i would require would be less than if i used it in the bath. So questions are as follows?-
1) What ratio do i dilute the stuff?
2) Will the acid eat the polythene i would be using to line the box?
3) Do i need to empty and re fill the box regularly?
4) Do i need to treat the surface once out of the bath to stop future rust coming back?
Cheers
Steve