If this place started with clay pipes and sat unused for several years (which would allow the sewer lines to completely dry out, possibly causing more shifting of the individual pipes) then I think this is on you, not the tenant.Replace the whole line. 

I would do a thorough search of every piece of dry wall and any other surface that is around the shower and go look at it in the attic as well.Generally speaking there is only a handful of mold types that are dangerous.

I don't want to be 'high and dry' with their issues and non-payment. 

There's even some late investing strategies our clients use to reconvert to rental then sell later and buy passive 1031 opportunities to hold till death and the step up in basis.The key points to remember are that delay of taxes (paying homage to watching paint dry and the World Cup here) is still a very valid strategy. 

I always felt like the house was dry but the humidity meter showed it was fine.My husband then changed out all the recessed lights to airtight lights and on a few of them they used fire safe caulk.

If they have more than one bathroom this would work as it has to dry a couple days at least, if not have it replaced to keep a 13 year tenant happy.

I actually suggest a laser printer, the thing about low use with the inkjets is the inkjet cartridges dry out easily, and/or they "self-clean" which is where they just use up their own ink, and the cost of the ink is a total scam. 

In this case the power would flow through the unlucky person drying to dry his clothes.

Or were they left high and dry once the check cleared???

Here's what I need help with:1) What's the best way to get the area between the roof and ceiling dried out?