The key to successful MF investments seems to be in good screening of your tenants.

Well some issues can be avoided by carefully screening potential tenants.  

We have spent several $$$ patching up holes and cracks around the property.

There are a million things that could go wrong from a drywall screw penetrating a plumbing line to improper site grading, missing screens, doors/windows not opening correctly and on and on and on.

I had a tenant accuse my contractor of smoking crack in the house and demand I decrease rent 

There usually is no screening process and unscrupulous owners or slumlords just slam bodies into rooms..often renting by the week.

I was thinking along the lines of a tank that's cracked or fallen to pieces or something of that nature, and tree roots would have been a great example.

He was asking questions that were clearly in the post that he didn’t read and proceeded to ask me “when he could move in” and I mentioned that he has to do the same pre screening process as everyone else and that I am not showing the unit yet. 

The water must come from some crack in the basement side or some or something similar, because there are not external windows or doors on that side. 

I've learned from bitter experience to screen like crazy (including home visit) before signing a lease, to ensure the tenant knows how to keep up a property.