Always make sure your driptray is completely cool before cleaing!
To make sure your driptray stays in the best shape it is the best to clean it after each use with a little soapy water. You can also just place aluminium foil in the driptray and replace this after each use.
Putting some river sand in your driptray, or special sand which can be bought at specialty stores can prevent small flare ups and grease fires in your BBQ. Just put a little on your driptray or on the aluminium foil.