I have had may 36 Hybrid Lang for just under a year. I smoke nearly every weekend. By far I smoke more often with the drain closed. The reason is because I fill the reverse flow tray with water. Yes, you will burn through more fuel because you have to heat the water. I had difficulty keeping my temperatures down when not using water in the tray. I've since learned how to correct that problem. The main advantage to closing the drain and adding water is the steam that it produces to keep my food very moist. It also aides in keeping the sugary rubs from burning due to the high humidity level within the smoke chamber.
If you have ever seen Myron Mixons' setup you will see that he swears by the water in his smokers. I do the same.
Lastly, make sure that your unit is level with the firebox end just below level. (I use a level inside the smoker and rest it on the RF plate to level it but it's easiest to just add water and make sure the water level is even with the bottom of the grate). I'm not sure how much water I use to fill the tray. I just fill it to within 1-2" of the bottom grate. You'll be surprised how little the water evaporates during the smoke. I generally refill the tray about every two hours with one gallon of water.
When I start my preheat my smoker it takes about one hour to get up to temp with or without the water. It seems to make very little difference.
You can tell the benefit of using the water in the tray when you open the lid during a cook. The steam is very evident when you lift the lid. You will also find that your chickens and turkeys will be the moistest that you have every eaten.
Sorry for the late reply.
Hope that helps,
WC
