Looking to connect 4" vented stack to another 4" stack using that stack's vertical clean out
Need to do this to save money because horizontal sewer line (off of stack #1) is cracked and is embedded in concrete slab in basement
Read in another post:
"you might have some clogging and back ups, due to the fact the clean out is a tee and not a y fitting"
How much of a problem is that?

"Need to do this to save money". Yeah, and this makes you different from any customer we ever have, right? C'mon, that's a pretty lame excuse 'cause I don't know any customer that doesn't want to say the same thing when it comes to these things!

With that being said, you are telling us that you are not pulling a plumbing permit and you are not going to do the job correctly. All I can tell you is that IF you can find a threaded adapter that can fit into the clean out you can do whatever you want. If you can't find a threaded adapter then you have no choice but to cut into the stack and install a WYE fitting.

Back to you...

Mark