The biggest concern for this dwelling going forward would be tenants and foreign objects being flushed or using the correct type of laundry detergent. 

Paraffin wax comes from petroleum, as do fertilizer, pesticides, herbicides, detergents, phonograph records, photographic film, furniture, packaging materials, surfboards, paints, and artificial fibers used in clothing, upholstery, and carpet backing.If people aren't buying those goods due to not having money...it's still going to keep oil down.Major issues arise with one economy countries (like those in OPEC) who live and die from oil.

They estimated $98,000 for the job and wrote this, basically saying that it's impossible to fix without also replacing the drywall and insulation, and that chemicals and paint would not be enough:"The odors and residue from the smoking are very apparent and appear to have permeated all areas of the Residence to such a level that these odors and residue, that is oil based, cannot beremoved by means of scrubbing with a detergent solution, application of a deodorizing solution, and application of a stain blocking type paint. 

Pretty good system and we have been bone dry ever since.Part of that process involved removing the drywall up four feet from the floor and while it was removed I scrubbed any areas that looked dirty or moldy on the cinderblock in accordance with CDC guidelines for mold removal (actually double their guidelines since I scrubbed it with bleach and water once and then a few days later again with detergent and water).  

Mix a solution of 40% bleach 60% water and add 1/2 cup of dawn dish detergent .

Drop or two of detergent in the water.

If you Google this, there's a lot of suggestions:1) Super clean by Castrol2) Let kitty litter sit on the stain as long as you can then after you wipe up try some ultra dish detergent to let sit for a few days3) WD-404) Oven cleaner

How about grading roads, picking up trash, mowing, flipping the bedrooms, sheets, towels, pillows, mattresses, silverware, detergent, new vacuum cleaners, etc. 

You should also have a dishwasher with detergent and a rule- all dishes cleared up.5) In general run this like it is an Airbnb. 

They may as well be trying to re-sell boxes of detergent out the back fo their vans (assuming they're old enough to get a drivers license much less a RE license).You sound smart, just promise you'll learn to do things the right way and not rely on subterfuge.