Since I make several sauces for brisket that use the juices as an addition or a base (and serve it au jus as well), I require lots of juice. To facillitate this, I foil at around 160 an add beef stock (or stock mixed with wine). This gives me plenty with whick to work and is well-flavored. I know many people don't foil briskets during the cook but this approach works for me.
To answer your question, Jack, about drippings that are rendered during the cook: fatty? yes; useless? no. Though it might be more trouble to you than it's worth, you can collect them for other purposes--as an addition to some pâtés (if you make your own), as an addition to the oil for cooking french fries, as a smear to spread on overly trimmed brisket flats instead of using bacon. There are a few considerations (straining, cooking off the liquid, tasting--the more trouble than it might be worth part), but if you're interested let me know and I'll detail those issues.