I had one recently that I couldn't clear with a snake, chemicals & water pressure etc.

@RichardCrouch, I just used Shawn Huss at Chemical Bank for a refi on one of my rental properties in Memphis. 

The contractor that we've been working for month has had AC coil replaced to a new one as well as organic chemicals sprayed into the system, the procedure was performed three times and helped for a short period of time.The issue that is being described here is also known as "dirty sock syndrome". 99% of the time it's getting solved with coil replacement.

Our local economy, by my estimate, is about 20% shipping/imports, 30% fuel production, and 60% petro-chemical (plastics, clothes, 95,000 different chemicals extracted from oil, etc).

I am a 'retired' chemical engineer looking to become a Real Estate Agent/Investor in the Tampa, FL area.

Sealing cement floors is a toxic chemical heyday.Discovered that I could then change the "use" with the city from industrial to residential.

They cut out two holes (one is maybe 2x4 and one is maybe 1x1) to dry it out and sprayed chemicals to prevent mold, and then the holes were patched up and ceiling repainted. 

If you get a lender involved (and even if you don't) you should get a couple of things:1) Geo-Tech study - This is for the soil to be stable enough to build on2) Phase 1 Environmental - The person doing this will search title/recorded history for things like buried storage tanks or uses like businesses dealing with hazardous chemicals. 

Then they treat the tub with chemicals then with color coating.

When I say tools, I am broadly including processes, chemicals, machines, etc.