ON THE OTHER END of plumbing is vent pipes, and waste water pipes (mostly black PVC) carrying waist water from building to the city street sewer linesI have heard of landlords having the entire building snaked (roto rootered out the pipes) once a year as a preventative maintenance measure, as many tenants pour grease down kitchen sinks, and wet- wipes (flushable wipes are very hard on plumbing) down toilets causing back up clogs.Most of the leaks on the waist lines are in the p-traps, toilets, clogs in the main drain line and sewer back-ups. 

We have had a few hiccups along the way with an old fireplace that prevented us from opening up the kitchen/dining wall to create a big open space, and so we've had some design changes out of the gate, but still moving ahead.

I do want to provide a safe living space, so I'm doing what I can to prevent bat visits from reoccurring.

You are allowing them to effectively buy good credit with you, vs. meeting your pre-established standard.Having said all that, there is nothing to prevent accepting a multi-month rent payment when their second month becomes due.

They may have a clause in their mortgage that prevents them from selling to someone else while they still owe the bank.

Check to see if zoning or HOA rules, if any, prevent you from subdividing the lot. 

Most of the COVID programs allow for back rent to be paid to prevent eviction.  

I see it as just another stumbling block and preventing people to actually get started.

And then the rent becomes very expensive after that to prevent holdover?

Here in Georgia we've not hit the problem but the leases I have do contain a clause that if the temperatures go below freezing the tenants are required to allow faucets to "drip" during the night to prevent pipes freezing.