I have never heard of using juices.
I have poked holes in the roast and crammed in garlic cloves then added a few whole onions and seasoned w/ S&P, and used a large can of Ccream of chicken soup poured undiluted then cooked in the crock pot. Cooking it this way you have instant gravy for mashed potatoes.
I also have cooked it the crock pot with sauerkraut and a can of beer. You can add a little diced onion if you like.
You can cook in the crock pot with BBQ sauce and after is cooks you will be able to pull it apart for pork BBQ sandwiches.
I use pork alot, we like it better than chicken and it is as lean as chicken ( we only use boneless, skinless breast) sometimes we can get the entire loin at Sams for under $2 a pound.
When I get it this way I slice off some chops and and use the other end for roasts.