Vent location for rear outlet toilet

[Sore Thumb Bob]

Hello all. I'm installing a rear flush toilet in a new bathroom adjacent to a small sink. The vertical down pipe is 15 feet away and the slope is about 7". There will not be a mercinator. Do I vent at the down pipe or just behind the toilet wall?

Thanks

 

[Reach4]

It can go a short way or long way under IPC. The vent is often a wet vent from a lavatory.

The house does need at least one real roof vent-- in other words, it cannot be all AAVs for venting.