The wooden floors were last refinished in 2020 (have all receipts), last tenant move out in 2022 with no issues to the floor (have pictures from move-out inspection),  2023 move out - large parts of the wooden floor are covered in black chemical residue (maybe from cheap rugs?) 

We have a lot of oil field service companies, chemical additives for oil wells, drilling pipe, motor rewinding, dirt contractors, construction/moving equipment, rental equipment, workover rigs, consultants, etc.   

Amongst all sorts of chemicals it also was corrosive enough to dissolve the lead pipes natural passive layer of PbO2 inside the pipes, so lead could leach into the water.

Additionally, efflorescence doesn’t mean there is water actively in the house, but that moisture is pushing ground leached chemicals through the foundation.

Beware that this process is very smelly in a chemically kind of way and you'll probably want to make sure that nobody else is in the house that day.For carpet and granite, I use Carpet Exchange. 

Vacation Rentals 30,000 to 40,000 per mo winter rents, approx 1/2 that amount other seasons. 5.7 acres with 6 SFR's totaling 10,000 sf living, Expandable by 50%, Covered RV spaces, Own Wells so pure fresh water with no city chemicals only costs $60 per month for all the homes!

I went with Shawn Huss @ Chemical Bank.

My duties include painting the runway's (close to 4000 gallons of paint a year) we provide security, ARFF services, snow and ice removal put chemical down on the runways and provide airport conditions for FICON notems.

Tenant agrees not to use caustic drain cleaning chemicals in any of the drains or plumbing fixtures.

He most likely abused the plumbing system letting hard waste going through the line and most probably used harsh chemicals such as drainex causing these issues.