Holding Tank Roof Vents

[cottonakin]

I bought one of those vortex type roof vent caps to hopefully improve the venting of my Black Tank odors. My 32RL has three holding tanks, one black, two grey and, of course, three roof vents.

Can anyone tell me which roof vent corresponds to the Black tank? I know I could get up there and let my nose lead me but would like a little assistance before it comes to that.

I'm tempted to assume the roof vents match the drain valves (in order from the front of the trailer to the back) but before I get everything up on the roof, I wanted to reach out to all of you wise companions that have always been most helpful to me in the past.

For what its worth, the drain valves are in the following order:
Black, Grey, Grey

I tried to find a diagram/schematic in the documents section but didn't see anything that appeared to be what I'm looking for.

[dagst1]

Just by looking the floor plan i would guess its the one closest to the front of the camper.

[Stan]

You could listen to the tank from the vent and have someone flush the toilet. You should hear a telltale sound.

[Photobob]

I concur with dagst1 the one closet to the front using the toilet location.

[Lloyd]

Normally the vent stack for the black tank comes straight up from the tank.