I like to start with the least caustic chemicals and the least abrasive scrubbers first then work my way up.

There are synthetic & rubber underlays for sound treatment as well, but they are very pricey and in our limited experience do not work any better than cork.I am curious about cork under ceramic/porcelain tile.  

Is that real stucco or synthetic??

As long *** there aren't any dry cleaners, chemical manufacturers or gas stations close to you, there is likely not an issue.

It often corrodes from the inside, especially in hot water lines since the warmth speeds up the otherwise slow chemical process.

@Al Williamson A chemical, composting or incinerating toilette would be less hassle, though it would probably take more time to train the tenants.A macerating toilet is definitely not tenant proof.

Or, do you try those chemical solvents that you lay on the caulk?

I will use mold remediation chemicals and paint throughout.  

I add a chemical designed for cleaning steam boilers to the water before starting the system.

I currently work as an engineer in the chemical industry (~7-5 salaried job).