First make a brine. In a medium saucepan, mix together first six ingredients on the stovetop. Stir until sugar dissolves; allow to cool. Add your pork loin to the mixture. Meat should be just covered, add water if necessary and refrigerate for at least a day; two days is better.
Remove pork from brine and wipe with paper towels and allow it to come to room temperature. In the meantime, oil grill and heat to medium-high heat. In a medium-sized bowl, stir together oil, garlic, thyme, and rosemary and brush on your brined pork.
Place pork on the grill and turn down to low. Turn to sear on both sides then only turn occasionally. Cook to an internal temperature of 140 degrees to 145 degrees. Let rest 15 minutes before carving.