I just purchased a disposable chafing dish at a party store. I plan to use it for a party we are having this weekend. Does anyone have any tips on using this? I have never used one before. It has a large aluminum tray to put water in and then two smaller aluminum pans to put food in. Two sterno candles go under the food. Any helpful hints would be appreciated. Just wondering also: how long does the water last--a couple of hours before evaporating? There are warnings not to use the sterno without water.