For the dressing: In a bowl, whisk together the mayonnaise, ketchup, relish, vinegar, celery seed and hot sauce, mixing well. Then blend with the sauerkraut and hold.
For the burgers: Preheat a grill to 350 degrees F.
In a bowl, blend the beef, corned beef and pork by hand, mixing well until evenly and thoroughly mixed. Next, portion the meat into 4 equal patties and sprinkle evenly with salt and pepper on both sides. Grill the burgers on the first side for 5 to 6 minutes, then flip and repeat grilling on the second side.
To build the burgers: Heat a pan over medium-high heat, add the butter to the pan and brown the rolls one at a time, repeating the process until all the rolls have been browned. Then place the dressed burgers on the bottom buns, finish with the bun top and serve.