Here's what I have:
It looks like you were between the engines looking forward to stbd of centerline at the area to stbd of the fwd entry door.* That line that passes under your electrical access door is where my line runs from the head to the top of the tank.* It's hard to tell from your pictures where the lines run.* All of my lines downstream of the tank, vent and pumpout, run to port.
Along with replacing that vent fitting, I would replace all those lines with white sanitation lines.* I bought a copy of Peggie's book that helped me work through some issues.* I highly recommend it.* Maybe she'll even chime in here with some sage advice.
This thread has much discussion about the issue.* Maybe it or other past threads will be of some assistance.*
I hope this helps.* Keep us posted on your progress.*