Take the corned beef and remove the extra fat. Rinse the beef thoroughly.
Pour the onions, potatoes, peppers, and garlic into the slow cooker at the bottom. Keep the corned beef brisket upon it.
Drizzle up some mustard seeds and add up the preferred seasoning blend.
Stream in the dark beer, and afterward, stream enough water so that the brisket would be completely submerged.
Add hot mustard, swirl a little and cover it up.
Cook it for six to seven hours at a high temperature. If you cook it on low, cook for 8-10 hours (The cooking time would be affected by the size of your brisket).
When the brisket gets considerably tender, take it out and keep it on a tray, pair it up with some potatoes. Cut the corned beef brisket in the opposite direction to the grain.