Gather the ingredients and put liner in crockpot.
Combine flour and black pepper in a large bowl. Dredge rump roast in seasoned flour and cover evenly. Shake off excess.
Melt butter in a cast iron pan over medium-high heat. Brown roast in melted butter on all sides. Place in crockpot.
Combine condensed soup, vermouth, and soup mix in a small bowl; pour over roast.
Cover and cook until desired doneness, about 8 hours on low. An instant-read thermometer inserted into the center should read at least 145 degrees F (63 degrees C) for medium doneness.
