slip grate into gallon size ziploc bag. Do not put any holes in bag. Pour 2-3 T. ammonia into bag. Seal bag & let sit for 12 hrs. Do this overnight. Take grate out of bag in kitchen sink. Rinse the grate thoroughly and scrubb with a nylon scrubber.
The Dawn/Vinegar solution removed soap scum so well I decided to try it on our nasty drip pans. Works better than anything else I've ever tried! Here's what I did. Fill sink with 1/2 cup Dawn Soap, 2 cups boiling vinegar, 8 cups boiling water and the rest just hot water from faucet. Soak for 30+ minutes. Scrub away the nasty!