Anything you say can and will be used against you in a court of law.Frankly, I assume that everyone who contacts me is a "tester" and I'm alway conscious  of making sure that I treat them the same as anyone else - even if it's a Section 8 renter who wants to buy a mansion.

I think the best approach is to assume that the ENTIRE scenario was fueled by emotions/hormones, and make the conscious decision to block that out.

Make sure the tenants upstairs are aware of how easily it travels down and stress that they must be conscious of the noise they make.

Whereas with a regular purchase, you'd have this done up front and know in advance of purchase whether there are serious environmental problems.

The unit has also been tested for environmental issues and moisture was below "dry levels" and indoor air quality levels were okay though CO2 levels were just above guidelines in some rooms.The tenant is known to use a lot of candles, we're wondering if this could cause this.Does anyone have any ideas?

Most tenants are engergy-conscious, but some aren't.  

@Sonia Spangenberg If the city is giving you issues, you could ask them if you gave them an environmental report showing that the land is safe and added septics is doable and won't harm the water table that might get them to calm down. 

Ranch land, farm land, land with preservation easements or environmental easements, land for wildlife, water, air, mineral rights of land, land for development and subdivision, and general land use of all kinds.

For a name-brand conscious landlord, there is even a Kohler for $150, but I wouldn't pay that much for a rental toilet. 

(*Note: we waver on the slightly neurotic side when it comes to environmental health - I'm sure most people would be totally fine living in this county, plus our soil tests showed totally normal levels of heavy metal exposure.