When my husband's Grandmother died, I was the designated person to bring this to all holiday dinners (even though I'm Irish!) since I learned what to do by watching her. She always used fresh rather than smoked Polish Sausage.
Bring sausage to boil and simmer 15 minutes; drain and set aside.
Cut bacon into small pieces.
Begin browning, then add diced onion.
Saute together until bacon is almost crisp.
Drain mixture, reserving bacon grease.
Drain sauerkraut (do not rinse).
Add sauerkraut and brown sugar to bacon mixture.
Mix in about 2 Tablespoons reserved bacon grease and water.
Place in large casserole dish.
Cut Polish sausage into 3" pieces and place on top of sauerkraut.
Cover and bake at 325 degrees Fahrenheit for 1 hour 15 minutes, checking sauerkraut mixture halfway through to add more water if sauerkraut appears very dry.
Finish baking; remove from oven.
Taste sauerkraut and, if desired, adjust flavor by adding salt and pepper, or a little more brown sugar, vinegar or bacon grease to your taste. (Note: In the old days, Busia (Grandma) would soak a cup of yellow peas overnight to soften them and would mix them into the sauerkraut. It was probably to stretch the quantity, but I don't do it anymore!).