1. Use a stiff wire brush to scrape away any loose debris from the grill and grates, and then remove the grill and grates.
2. Scoop out any ash at the bottom of the barbecue.
3. Clean using dishwashing liquid, water and a plastic scrubber (not abrasive cleaners and metal scrubbers). If your barbecue does not have a painted, non-stick or an aluminium surface, clean the inside and outside of the barbecue with baking soda (or another abrasive cleaner) and a little water using a metal scouring pad.
4. Place the grill and grates in a large plastic bag and cover them thoroughly with oven cleaner. Allow them to sit for several hours or overnight. If the grill and grates are aluminium, soak them in dishwashing liquid and water instead.
5. Remove the grill and grates from the plastic bag and place them atop several layers of newspaper.
6. Use a metal scouring pad or stiff brush to scrub them clean. If the grill or grates are aluminium or non-stick, use a plastic scrubber, not a metal one.
7. Hose off the grill and grates to remove any remnants of the oven cleaner. Use the hose to clean out the barbecue itself as well.
8. Allow everything to dry thoroughly before replacing the grill and grates.
9. Coat the grill with vegetable oil to prevent rusting and future build-up.