whats the best way to clean out a header tank ?
i got one from a scrappy in good condition but the bottom of it has brown stuff stuck to it
i want it looking mint how do i clean it ive tried filling it up with boiling water and flushing it through . and i cant get a tooth brush into all the areas. i thought about putting it in the dish washer lol or is that just stupid

or am i just being too fussy and the brown stuff is just somthing i have to live with. its a fiesta mk3 header tank

cheers james