Place meat in a very large roasting pan on top of stove or a big crock pot, 5-6 quarts).
Dump the drained sauerkraut on top of the meat. On top of that, empty the box of sugar. Next the tomatoes and liquid. Place the onion and apple pieces around the meat. (I keep the meat on the bottom and kind of mix everything else around and on top of it, opening the pot after half the time to mix again and break the meat up into pieces).
Cook in a crock pot on low for 4-5 hours or high for 3-4 hours. You can also cover and cook in the oven at 350 degrees or on stove on low-medium. The meat needs a few hours of cooking to shred and combine with other flavors, so check and stir occasionally whichever heat you choose. Cook until the meat falls apart into small pieces, and the sauerkraut just about disappears.