How long did you cook your brisket? In your last hour you can crank up your temp to help with your bark or you can run a dry water pan and crank it up to about 350 and do your brisket. It will take a lot less time so monitor your meat temp closely.
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Search for Old Dave's posts he has information about running at high temps with a dry water pan. It's very hard to run over 250 with water in the pan as the water boils at 212 and wants to maintain that temp. Have you ever put a paper cup with water in it in a fire and watch it. It will not burn the cup until the water boils off. It will burn around the edges, but not where there is water in the cup. Your BWS is like that if you have water in the pan and crank up the heat it just boils faster and faster trying to keep the temp down. If you have meat on the lower rack it will wash all the rub off it is boiling so hard.