if the vent starts deteriorating this can happen with partial blockages.

We've had calls for HVAC problems, plumbing blockages/leaks, electrical issues, (not light bulbs!) 

At least then, when it has to pump, water will get out rather than come back due to sewer line blockages.

@Brie Schmidt...lol....maybe in the wall..when it's backing up in the tub, there is a blockage somewhere...The camera is worth the extra cost when it's not obvious...what about the pressure?

It's been about 20 months since the work was done, and there has been zero problems with any sort of blockages or sewage back-ups, for a basement bathroom. 

I looked for blockages in the chamber and that looked clean and the burner itself with flame looks very strong.

They went out of town for 2 weeks and it was heaven, this place was totally liveable, I would have had party but my cat died, probably from stress induced by one of their screaming battles, but actually from a urinary tract blockage that would have cost over a thousand to correct (which is known to be caused by stress) anyway.

A couple of years ago I had a sewer line dug up where the camera showed a blockage.  

Jay, it sound like you have a blockage in your shower drain.

But remember that clause in the lease about how the tenant is responsible for foreign object blockage in the plumbing system?