However, as long as you do makereadys with more durable materials like snap in floors instead of carpet, flush lights instead of fans.. you're safeguarding yourself against those costs. 

Continue to flush the unit thoroughly with water (lukewarm if possible) after you run your waterbased paints. 

-Clean Dryer Exhaust Ductwork-Clean Refrigerator Coils-Clean Dishwasher-Clean Shower Heads-Inspect Sink & Toilet Fixtures for Leaks-Replace Air Filter-Re-Caulk Tub/Shower & Bathroom Floor-Flush Water Heater-Lubricate Garage Door Bearings-Replace Batteries in Thermostat & Smoke Detectors-Inspect slab for signs of termites; trench ground with Termidor every 5 years

So much drama and nonsense (literally had one tenant deliberately flushing tampons down the toilet to clog the sewer line and get back at me for throwing her out)  I got it under control and it's probably my best performing property from a numbers perspective, and I haven't visited it in years. 

Great ideas above, just to condense everything and add a couple more ideas:Low flush toilets and Low flow fixtures (showerheads, etc.)LED Lights and more energy efficient common area lights, if applicable.Replace windows with energy efficient windowsImprove insulation in the attic and crawl spacesRecaulk windows and make sure all doors are sealing well when closedUpgrading appliances, water heaters, etc., if they are extremely energy efficient.If higher quality property, consider installing nest thermostats to help with energy savings since tenants won't care if they aren't paying the billI'm sure there are many more but those are a great place to start and get the bulk of your savings. 

My tenant has been flushing non flushable baby wipes down the toilet for an unknown period of time.

You can gauge some of the big stuff yourself, the rest you can leave to a good home inspector to flush out.  

Motion detector switches,low flush toilet, led bulbs, coin or no laundry,No a/c, extra insulation in attic etc.Well aware of up front costs just curious if anyone had explored the r.o.i.

They are flush with cash - like almost 10% of current share price is held in cash.

There have been a couple of very minor things.We put a sign on the back of the toilet telling people to only flush toilet paper(due to a pump system that goes to the city sewer) and a small basket with 2 starter soaps and shampoo's.