Using a pipe hub donut to join 3" PVC to 4" Cast iron pipe.
I tried using a 4"x3" half pipe donut to join a 4" cast iron pipe and a 3" PVC but its too big. Then I tried using 3"x3" and that one fits good but not really snug. Is there a good epoxy I could use or an alternative you recommend? FYI: I don't have an option to change the cast iron pipe since its embeded in concrete which I can not break.
Look for a 3" SV gasket. You will have to bevel the outer edge of the pvc. You will need liquid soap to soap the pipe and gasket. Assuming you have already removed the lead and oakum from the cast iron hub.