Where my 4" cast iron sewer line exits the house there is a 4" combination
wye and 1/8 bend hub then it dips down and go under the concrete driveway.

This 4" SV CI hub serves as the cleanout from that point downstream. There
has always been a 4" test plug in that hub. Why not a real cleanout I don't
know and I intend to rectify it.

I know I can get a 4"x4" PVC donut gasket and then put in a 4" cleanout
adapter.

However, I prefer to use metal parts if at all possible, brass or cast. I
went to Charlotte Pipe web site and tried to see if I can find the right
parts but I do not see a part list. I think I need some sort of a
adapter...for a 4" SV CI hub, that has a threaded ring on the inside for a
full size cleanout plug. I don't know what this is called...I think to
install it I would need to either epoxy it to the existing CI hub, or
someone who is skilled to use oakum and pour a lead joint, then I can insert
a threaded metal plug. Does anyone have an online source where I can see
the parts with pictures?

Also I did find a 4" brass plug. It's over $120.00. Is this highway
robbery? How can it be so expensive? Are the cast iron parts cheaper?

Thanks,

MC