Prepare pot roast vegetables: cut potatoes in half (or into quarters if large), onions into ½-inch wedges, and carrots and celery into 2-inch pieces; set aside.
Combine gravy mixes, flour, salt and pepper in large bowl. Add vegetables to bowl; toss to coat well. Remove vegetables from flour mixture; set aside. Place vegetables in 5 to 6-quart slow cooker. Add beef Bottom Round Roast to bowl, turning to coat evenly with flour mixture. Remove roast and place in slow cooker in center of vegetables.
Whisk beer into remaining flour mixture until smooth; add to slow cooker. Cover and cook on HIGH 6 to 7 hours or LOW 9 to 10 hours or until beef and vegetables are fork-tender. (No stirring is necessary during cooking.)
Remove roast and vegetables. Skim fat from gravy. Carve roast into thin slices. Serve with vegetables and gravy. Sprinkle with parsley, if desired.
