A rump roast is cut from the bottom end of the beef round, often including both the top and bottom round, though sometimes the bottom round is labeled as simply a rump roast. Butcher's twine is useful for tying the roast and maintaining a neat, uniform shape. The top and bottom round portions of a rump roast often separate while cooking as the fat layer between the two portions renders, but string can hold them together. If the bone is removed, the roast might lie flat or uneven and looks better when rolled and tied in a round shape.
Trim away any excess fat from the outside of the roast, particularly the thick, hard fat. Some fat left on a roast is good for keeping the roast moist and flavorful.
Roll the roast into a uniform round shape with the rolled ends tucked under the roast. If the roast is wider at one end, roll only the wider end so it matches the narrow end.
Set the roast on a cutting board with the narrow end facing toward you. Slip the butcher's twine or similar string under the roast, bringing the ends on top of the roast, about 1-1/2 inches from the end. Leave a tail of at least 4 inches on the short end of the string. Tie the string with a basic square knot tied tight enough to hold the shape.
Extend the long end of the string down the roast about 1.5 inches from the first tied loop. Hold your finger over the string at this position while wrapping the loose end of the string around the roast in a loop. Loop the loose end of the string around the string where you're holding it with your finger to complete the second tie.
Extend the loose end another 1.5 inches down the roast, loop it around to tie the third loop, and continue down the roast until about 1.5 inches from the end.
Flip the roast over, extending the loose end of the string around the roast. Bring the loose end of the string up through the loops on the back side of the roast. Loop the string through each twice before moving to the next tied loop on the rope. This mirrors the string on the front side of the rope that connects each parallel loop.
Tie the string to the loose tail on the first knot and cut off any excess.