Rump roast isn't fast food to prepare. Plan on at least four hours of cooking time and up to 10 hours to make it fall-apart tender. As you might expect, a rump roast comes from the back end of a steer. Also known as bottom round, this cut of beef needs to cook for a longer period of time in a liquid to make it tender and flavorful.
In a slow cooker, a rump roast needs eight to 10 hours on low heat to become fork tender, depending on the size of your roast. This may seem like a long time, but is relatively easy on the prep. Add 1/2 to one cup of water, red wine or beef broth to the pot so the roast doesn't dry out and you can walk away for the day. The liquid should partially cover the roast, but not submerge it. Keep the lid on the entire time.
To slow-cook a rump roast in the oven, set the oven to 250 F. At this temperature, the roast will cook in about four hours, depending on the size of your roast. Place the roast in an oven-proof pot or Dutch oven with a lid. Add 1/2 to one cup of broth or red wine, so that the roast is partially covered. Cover the pot with the lid or foil. Check the roast occasionally to make sure the liquid isn't simmering. Also take that opportunity to add more liquid if necessary.
Before you transfer your rump roast to your slow cooker or oven, you might want to consider browning the meat. Browning isn't absolutely necessary, but it will help seal in juices and create better flavor. Heat a bit of oil in a saucepan on medium-high or high and sear the roast on all sides, just until the roast is golden-brown, but not cooked through. Transfer the roast to a covered pot or slow cooker to finish cooking.
The first sign you'll have that the roast is done is the aroma filling the kitchen. The roast will be a dark brown color and fall apart when you dig into it with a knife or fork. Beef should be cooked to at least 145 F to ensure food safety, but to cook a roast until it falls apart, you'll need temperatures closer to 180 F.