i use a product you should be able to find at home depot called cleen strip phosphoric prep and etch to remove rust. $15/gal. good for old rusty tools also. not sure how it would affect the porcelain coating on the lid and bowl though. you might try leaving a rag soaked in some on a small test area. just till the rust is gone. same for tools. sort of leaves a parkerized type finish and helps protect from further rust.