I usually take one large onion and slice it thinly and place at the bottom of the crock, I then season a boneless pork loin (not shoulder or tenderloin) with salt, pepper and garlic powder thane place on top of the onions. I pour 1/2 a bottle of whatever BBQ sauce you like (I use KC Materpiece Original) and cook on high until it's done (depends on how large a piece of meat you use). I then remove the meat and let it rest, then I take the sauce & put it in a sauce pan and bring to a boil to thicken it a bit and then add the rest of the bottle of sauce and mix all that with the shredded pork.
Remember when using a crockpot that you should only fill the crock 3/4th full and the liquid should only come about 1/2 the way the food.