This recipe was our standard go to marinade for tri tip for the longest time. The Orange juice helps break down the meat and it comes out very tender. If I had to say that there was any downside to this it would be that the meat comes out with a yellowish tinge to it (orange juice and dijon mustard, go figure). The one thing I can't recall having is leftovers.
1 white onion (coarsely chopped)
4 cloves garlic
1 cup orange juice
3 Tbs Dijon mustard
1 Tbs salt
2 tsp pepper
Put all the ingredients in a blender and liquefy. Puncture the beef all over with a fork. I put the tri tip in a gallon freezer bag for less clean up. Marinate for at least 4 but no more than 8 hours. Cook on the grill on medium heat until the internal temperature is around 130° F. As with any tri tip let stand covered for at least 15 minutes after cooking. Slice in thin strips across the grain.