I don't want to chance it and what nasty residue is left on the walls that I will have to clean off. 

UGH.....got her to leave voluntarily basically just by starting eviction process....but mannnnn the mess they left me :-(Got the keys back Dec 1st10000's of dead fleas...bedbugs and spidersruined 800sqft of carpet....and patches of the hardwood underneathleft behind 20-30 boxes of junk and cupboards full of foodbedroom walls are so disgusting with bedbug and spider residue I have no idea how they were living therethey did leave me a fridge thats in nice shape though haLet the clean up begin !  

The oxidation process via the ozone generator will help neutralize the residue and odor built up in your vent system.  

It could be As simple as a specialty adhesive cushion/caulking type product applied before putting new drywall up, or maybe rubberized mounting strips or something.

If you use square trim you could stand the sheets of drywall up vertically, fire tape joints with self adhesive fire tape and cover joints with a 1" X 10" or 12" board similar to trim. 

. * Look for burns in the carpet and on places where one might rest a cigarette, such as a counter top or fireplace mantel.Note: Cigarette smoke will leave a yellow tar residue that can be easily seen in furnace filters and on cleaning wipes.

That's the first principal element of a quality cost segregation study. https://www.irs.gov/businesses/cost-segregation-audit-technique-guide-chapter-4-principal-elements-of-a-quality-cost-segregation-study-and-reportA "mini" cost seg is basically a residual estimation, which is cautioned against by the IRS because it is generally inaccurate.

Then on top of that we usually discover a heat vent covered in asbestos & full of old oil fce residue/dust, then we discover a run of random cast iron vent plumbing.

Ultimately I want more residual income and I'm thinking if I can get them a good return and could have a little residual income from each property that would be ideal!

We have been using an adhesive product from lowes called musclebound instead of thinset.