The Sirloin Tip is a great choice for corning your venison - the size is perfect for a family meal or making sandwich meat slices.
Put the onions, garlic, and spices in the dutch oven. If you will add vegetables later, use a spice bag, otherwise you will be getting a lot of flavor bursts later.
Add the roast.
Add the liquids. I like the roast to be at least half submerged, but am usually somewhere between half to three quarters covered, so add more liquids if you have a big roast.
Throw it in the oven at 250 for about 6 hours. Flip it once or twice during that timeframe.