Venting toilet

[John H]

Can a combination Wye with 1/8 bend be used to connect toilet flange to a horizontal main drain and use the “back side” of combo wye to connect to vent ?

 

[ExtraMilePlumbing]

yes

 

[Jamesplumbing06]

That’s called a dry vent. My IPC says no. But physically yes it works. Try to stack a sink on the vent coming out “backside of combo”. This “washes” the vent and changes to wet vent. Basically you don’t want a vent laying horizontal that never sees water flow.