Put out side on news paper spray with oven cleaner let sit for 1/2 hour then scrub with brush and hose
Take out side and spray with oven cleaner put on a plastic bag let set over nite then hose off. May need to repeat. Or use a scrubby to get the rest.
My favorite cleaner for this type of job is GP66. You can lay them out on newspaper then spray, let sit, then clean up.