Our cleaner wipes down the top edge every turn over, checks the pH with a test kit, adds the chemicals needed, and adds water if needed. 

They dump/refill it between guests and handle the chemicals, etc.  

I think I am going to respectfully disagree with you on this score sir, the excessive use of chemicals on our soil is yet to be determined.

I don't think "meth" the drug is a risk to a house, it's the chemicals that are used to produce it.

Likely with Chemical Bank.

Is there a gas station or dry cleaners nearby (dangerous chemicals could be underground)?

Instruct the tenants not to use chemicals in the toilet tank, especially chlorine tablets, as they damage flappers and other parts inside the toilet tank. 

We don't allow our tenants to use draino or any other caustic chemicals in our plumbing systems.

I'm chemically sensitive and short of breath.

Here is one of many articles, concerning that development:http://businessjournaldaily.com/economic-development/breaking-news-shell-chemical-selects-beaver-county-pa-cracker-plant-2012-3-15Raymond