Pour 1/2 cup of water into crock pot. mix sage, salt, pepper, garlic and 1/4 cup of brown sugar together. Rub over pork and place in crock pot.
Cook on low for 6-7 hours.
About 60 minutes before roast is done, prepare glaze: in a medium saucepan take remaining brown sugar, mustard, cornstarch, remaining water, vinegar and soy sauce. Mix together and heat over medium heat, stirring constantly until mixture thickens. (approx. 3-4 minutes).
At this point, I remove roast from slow cooker and put into an oven safe pan or foil lined baking sheet and brush on glaze and put in the oven at 350 and finish cooking until done, brushing with glaze 1-2 more times during the last hour of cooking.