It best to make everyone responsible for what they consume and if they don't pay, they bare the full consequence.

I also agree with the idea of talking with the tenant about the consequences of not using the fan and their action of intentionally disabling it.

Sometimes I think it's our job in the universe to provide someone with a consequence.  

Now, if she was stuffing "flushable" wipes, and we all know there really is no such thing, and you've explained to her that she can't flush flushable wipes and if it happens again and the snake brings up a wad of flushable wipes again - then she'll have to pay the bill - that's reasonable.But, to charge her for a problem because you can't figure out how it's happening - well, you'll end up with an expensive consequence.  

Or, you can flap your arms about what a meanie I am and do what you want, and pay the consequences.  

The reason for rules is because millions of landlords have proven, having screened 10s of millions of applicants that those ridiculous rules serve a very valuable purpose and those landlords that choose to ignore proven valuable tools included in the ridiculous rules will suffer the consequences. 

Those are the same regulations we are forced to work with in our jurisdiction and I choose to ignore them to protect my business and my tenants.You will learn from experience that :  enforcement of the regulations will be rare if not non existent, reports by applicants few and far between, proving their case nearly impossible and landlords will quickly learn to operate their business as they always have.Stupid landlords will tell their applicants why they were rejected and suffer the consequences while the smart one will operate with impunity by simply not being so stupid as to tell them they have discriminated.Ignoring the regulations is necessary to protect your business and your other quality tenants.

Secondly, I recommend you man up and accept the consequences of your actions.

But, in the adult world there are consequences for not following through on your contract obligations.Calling it going gangsta is a way to put humor into an expensive, bad experience, and taking the mindset that I'm not going to be a victim.  

While I suggest speaking with an attorney for the consequences of simply letting them move in, at the very least, you should screen the new tenant as you would for anyone else.