Branch connection under toilet flange via its vertical drain - what is allowed?

[Michal Krombholz]

Hi,

The existing toilet drains vertically for 2ft then to a horizontal main via a long sweep (no existing vents directly on/around toilet).
Is the connecting a horizontal branch to this vertical discharge from a toilet OK?
And if so, what connection type: san or wye tee?

/\
:
:
Y---sink
|             wc
|             |
\------------\|
              |
              \-------- MAIN

I am hoping for tapping into this for a wet-vented shower then lav drain of 2" to a dry-vent.


IRC here.

Regards,
Michal