I use clay saucer and no water.
I start with 8 hot briqs dumped into the middle of full basket.
If you can't get the temp below 275 sounds like you might have started with to many hot briqs.
I start with 8 hot,all vents open.When temp reaches 200 I close all vents in bottom to about 1/8 and it settles in to around 225.
Good luck...JJ