You mean the water was so heavy that it cracked the floor joists and the entire floor and basement ceiling fell in?

I'd personally say pulling your water heater out and replacing with a wall mount on demand one, would be worth the cost to have in unit washer dryer if you are staying there or renting it, it would be worth it.its always worth doing the big stuff well and correct even if you are cleaning up after someone, the long term hold always prevails, its just a little frustrating front sometimes, but hang in there!

This was a clean foreclosure property, which is usually difficult to find.

I know they are crazy guest friendly but this seems over the top.Guest didn't deny it....responded with "I payed the cleaning fee, why would I clean up?"

Start with one that might need some clean up and go from there.

The timeline is years for clean up and decades for reconstruction and recovery.

Because Airbnb only makes money when the guest books on Airbnb.Hence, they want the price to be cheapest on their platform, so people book on Airbnb instead of elsewhere, and want their properties to be able to compete with hotel prices (even after cleaning fee and service fees). 

With seller's permission: Unscrew the shower head and put it on shower floor.

That hard work includes making the investments that the current owner hasn't made (nicer kitchens, new flooring, fresh coat of paint, etc.), removing tenants and marketing to new tenants.

Even if it's cleaning rooms, get a feel for the operations.