I use the little 4 ounce stoneware bowls (Corningware) from Walmart in my 6qt tubs. They are on the baking utensils aisle in Walmart and come 2 to a package. Apparently only the larger Walmarts carry the 4 ounce size.

Steve

edit - They also come in 7 ounce and 16 ounce, which I use in my larger tubs.