I rent in a highrise apartment building. It can take upward of a year when asking the landlord to check for obstructions in the ventilation and/or clean the conduit, e.g., as might be prompted by lots of condensation after showering, leading to mold.
I have a sewagy smell in the bathroom, especiallly pronounced when I've kept the bathroom door closed. I fear that it might be the bathtub P-trap, as the sink P-trap was recently cleared of obstruction (after years of slow drainage -- I usually try to find work arounds for as long as possible before imposing on the landlord for servicing). Perhaps there is a leak in the bathtub P-trap, or there is a strand of something that wicks water out. I did not imagine that it would be trivial to pull up the bathtub to inspect this, and shining a flashlight down reveals that the drain pipe immediately dekes horizontally. If online images are any indication, it likely meets a vertical pipe for the overflow, and then curls into a P-trap.
Since I anticipate much resistance and delay to a nontrivial request to check the bathtub P-trap, I considered renting a drainage camera to look myself. They're quite expensive, with limited options in my city. Two offerings I found were for $220 and $150 per day. I also found that a hardware chain with continental presence (Canadian Tire) sells a cheap camera for $300 ("MAXIMUM Inspection Camera"). So I might just buy one at twice the cost of renting, which gives me the freedom to re-inspect if necessary.
Can such cameras typically see whether the P-trap is water filled, or is there an large uncertainty in their effectiveness? I don't want to blow $300 on a course of action for which there is (say) 50% chance of being able to see the water with some degree of certainty. I found a youtube video alluding to seeing reflection off the water in a P-trap, but frankly, I couldn't make anything out of it. If it takes a highly experienced eye to recognize such a reflection, or otherwise discern whether sufficient water is present, then that reduces the chances of effectiveness of this "solution" for me.