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Yes... most definitly...liquid in the pan...(unless you want burning fat smoke on your meat and in the pit). As long as the brisket will be on...your temps will equalize. I do usually try to leave plenty of space between the bottom of my cook (butts and brisket) and the drip pan.
You're looking to get good air circulation between the pan and meat if you can...and it will help with bark formation on the bottom.