There is a coded gate for access to the facility and it does appear to have security cameras though I have not visited it yet.

Install exterior and interior wireless video cameras that are motion sensitive. 

Be proactive , pay to have a camera run down the sewer main to check its condition . if it all looks good you are fine . put a clause in your lease that the tenant is responsible for clogging the sewer line .

If it surprises me and is worth a lot more than I expect, I may fly over there to try out the famed Memphis BBQ and maybe look at the house.Actually I already spent my forecasted profits and bought a new camera!

I don't really want to invest in a nice camera.  

A sewer specialist will inspect the system for you for about $200 and stick a camera in the pipes (drain tile).Drain tile can get damaged for example by roots (Willow trees are really bad and will go a loog way to reach the pipes), but sometimes its just age.The way you deal with the issue depends much on your strategy.

So, today I bought a digital camera and called some realtors.

Just last week, my usual plumber was away so I scrolled through my camera roll and found 3.

Get cameras and cooperate with your good tenants.

For people who do own apartment buildings of 6+ units now, do you contract ADT or some other online security system with cameras?