-You may need to find longer term accommodations for your tenants.Hopefully, you weren't foolish and trying to DIY manage it remotely on your own.

When we get awkward 2-3 week gaps and have to switch to an STR model, it's a PITA because we're cleaning ourselves.

Property operations: Deep cleans, air filter changes, moisture issues, hvac maintenance, etc..

Jan 18 noticed a water line in my stove after knowing I cleaned the same waterline when I purchased the home.

I can remember my college microbiology class where the first experiment was the professor having us bring in samples of cleaning agents (i.e., bleach, ammonia, popular cleaning solutions "guaranteed" to sanitize etc.) spread on Agar plates that were then incubated in a warmer. 

Does it really need to be replaced to pass a future inspection or does it just need work or cleaned?

We definitely will approach it with the standpoint of needing a team in place and not DIY-ing our way through it.

Anyway its a work in progress but if it has the desired effect of getting some of these friends of the tenants to clean up their act it will be a success.  

She has an established cleaning business and is expanding her services. 

Offer to refund his deposit immediately as long as there's no damage (you handle the cleaning).