Fill a large stockpot with 3 quarts water. Add the salts, sugars, honey, pickling spice, coriander, mustard seeds, and garlic. Bring to a boil over high heat, stirring often to fully dissolve the salt and sugar in the water. Immediately remove the pot from the heat once the brine boils. Let cool.
Combine the brine with 3 quarts ice cold water in the stockpot or any large pot that will fit in your refrigerator. Use two pots if necessary with the mixture evenly divided. Cool completely.
Trim the fat from the brisket until the fat layer just covers it and is no more than 1/4 inch thick.
Put the brisket in the brine and submerge it completely (I put cans of food into a ziploc bag to sit on top of them). If necessary, cut the brisket in half to submerge in two containers.
Allow the brisket to brine in the refrigerator for 5 days. Remove from the fridge once a day; stir the brine and flip the meat over making sure that all of the meat gets exposed to the brine.