Combine the water, brown sugar, kosher salt, peppercorns, and mustard seeds in large pot over high heat.
Stir until all the salt and sugar has been dissolved.
Add enough ice to cool the brine down to fridge temperature.
Place the pork into a gallon sized plastic bag and pour in the brine. Place inside in a bowl just in case the bag leaks and place into the fridge. Soak in the brine for 1 ½ to 2 hours.