Snag wrote:

Yours must be the vertical cylinder type . I've worn out two of those ...
now I use their horizontal type , with the firebox on the end . I've done
pork shoulders and turkeys that were almost orgasmically good . I failed at
brisket , but have learned from my mistake - ya gotta wrap it in foil and
let it rest over very low heat for a coupla hours.

Good grief, no. You *do not* foil brisket. There is never any need to
use foil on a brisket other that *after* it's done and it's going into
the refrigerator, or into a cooler to stay hot until serving.

The keys to perfect brisket are time and temperature. You smoke the
brisket around 275F for as long as it takes for the core temperature to
get up to 195F or so. If you monitor the temperature as it goes, you
will find that the temp climbs fairly linearly up to about 190F at which
point it plateaus for a while before finally starting to climb again.
What's happening at this plateau is the collagen in the brisket is
breaking down, and when the temp starts to rise again the process is
complete.

It is only after the collagen has broken down that you will get a
fork-tender brisket. For a large 15#+ brisket this process can take 18+
hours. If you don't want to tend a smoker for that long, you can cheat
by doing the first 6 hours in the smoker, and then moving to a regular
oven set at the same 275F for the remaining time. In the regular oven
you put the brisket on an elevated rack (roaster rack or similar)
sitting in a large rimmed baking sheet to contain the rendered fat.
Again *no* foil is used. Depending on how much you trimmed the fat cap
on the brisket, you may need to keep an eye on the fat level in the
baking sheet, and be prepared to remove some (turkey baster) before it
overflows.