I had a neighbor that laid his on the grass at night and the dew/moisture softened it so it was easily cleaned.

I have a charcoal grill and when I want to clean the grate, I take it off and spray it with Easy Off Oven Cleaner the day before I want to use it and prop it against a fence post. Next day I just spray it with the garden hose and it comes out shiney. If you are using the yellow can it is very caustic so don't get any on you or inhale the fumes. The blue fume free version will work but not as well.

The link below had a lot of good information.

Here is a link that might be useful: Serious Grill Cleaning Tips

There are several spray cleaners that usually used to clean my gas grill, easy off rec, carbona oven rack etc are some spray that usually likes to clean and simple and easy cleaning will increase its potential for cleaning for many years.

Just turn the grill on to it's highest setting and let it go about about 20 minutes. Scrape off any residue with a grill brush. Cook.