05-03 2 comp sink acting as wet vent

Question: 05-03Code Section: 7Date:OBC 2006 Reference:

Question: Can the 2 comp sink that is discharging through a grease intercepter serve as a wet vent for the hub drain?

 Interpretation: (On. Reg. 403/97) The short answer is no, Sentences & (2) describe how to wet vent fixtures:

Where 2 or 3 fixtures installed in a plumbing system, any one of the fixtures may be wet vented by one or both of the other fixtures and in Sentence (2) it tells us that: Where there are 2 wet venting fixtures and they are not connected at the same level, they must be separately vented.

At first glance most of us would fail the above example just because it does not look like a proper installation.  But then, after reading the Article on wet venting, we could get confused because it would appear that we comply with the Article; we have 3 fixtures, 2 fixtures are wet venting the third, both are separately vented and one of the wet venting fixtures is drained through a vertical continuous waste and vent.                     

So why are we still refusing it ?  The problem is that one fixture flows through another before serving as the wet vent and although the interceptor is not referred to as a trap, it does act as one and we feel that the continuous waste is on the wrong side of the equation when it comes to wet venting the hub drain.  Usually, separately vented means that both fixture traps have their vents connected to their respective fixture drains (see and, in this scenario, the back vent for the interceptor is on the horizontal branch ( this is compliant with Sentence