Which Roof Vent is most likely the Black Tank Vent

[RRman]

On my 3670RL, there are three vents, corresponding to the 3 tanks. One on the door near the shower skylight I suspect is the bathroom gray tank.
Two vents close together by the bath are likely the Kitchen Gray tank and the Black tank vent.
Anyone know for sure which is which?

Or do I need to fill and let my Black Tank get stinky and try to sniff it out?

My purpose is to install a better aerodynamic vent from "Coil'n'Wrap" and hopefully alleviate some bathroom stink issues after several days of black tank use while camped long-term.

Thanks!