PVC Into a Cast Iron Cleanout?

Hello-
I'm installing a macerating unit and need to connect its 3/4" PVC effluent pipe to my soil stack, which is 4" CI. The stack has a cleanout wyed into it - which seems like a good place to make connection (is it? ). I'm thinking I'd just place a 4x(1.5???) PVC wye where the existing cleanout is, and just add a cleanout to the end of the new wye, connecting the 3/4" pipe to the smaller part of the wye with a reducer. Is this possible?
It's hard for me to tell exactly how the cleanout is connected with CI. Is there a cleanout plug and cap which fits into the wye, just like PVC? or does the cap just sit in the wye itself? Is it threaded like PVC? It looks like there is lead & oakum around the cap, but i can't tell exactly - it's been coated a few times with some very thick paint.

Any advice on how to connect the 3/4" pipe to my stack would be greatly appreciated.
I'd reeeeeealy rather not cut out a section and brace the whole thing, since this is in a basement and there are 3 stories of 4" cast iron above it to support

Thanks!

What is a macerating unit? Never heard of it.

From your description, the cleanout fitting may be 3 1/2" ips, and if so, it is impossible to find ANY fitting which will screw into it.

Hairyhosebib said:

What is a macerating unit? Never heard of it.

Click to expand...

http://www.saniflo.com/

Try this link, should answer your question