I am trying to connect 2'' PVC pipe to an existing cast iron (CI) hub. The inner diameter of the CI hub is about 3-1/4''. The same question was asked previously by someone else (https://terrylove.com/forums/index.php?threads/donut-sizing-for-cast-iron-pipe.68307/) but no final solution was posted. He tried three different size of donuts 3'' hub to 2'' PVC and 2'' hub to 2'' PVC (Fernco 33U-205, 22U-205, 22UX-205), and none of OD of those donuts would fit tightly into the 3-1/4'' ID CI hub according to him. He also tried oakum and solil-o and failed the inspection. Does anyone have the same issue?