I'm trying to stay level-headed and unemotional about it (it's not going to kill my deal regardless), but this doesn't pass the common sense test.  

With Shelly on edge, I knocked on the door, prepared to negotiate with someone who didn’t know us and wasn’t necessarily open to leaving.

At the end of the day your objective is to prevent liability events from occurring and if they do, to be prepared.  

Fix that and re-test with a hose...

"One or more of the sink drain lines had leaks under them when tested.

Once you've established a solid team of property managers, contractors and lenders, you'll be well-prepared to take on more complex strategies like BRRRR.

It took me weeks to prepare.

Start doing category 1 items right away, provide notice and do category 2 as soon as you can and finally prepare and get ready to initiate category 3 items based on your ability to handle them. 

I'd say go in person to the PO when you mail, so you can get a receipt...that shows when you mailed in a reasonable way....I notice when you have a nice file when you go to the eviction hearing your chances of winning seem better if the tenant shows up...because chances are they will not be prepared. 

Once you have a shortlist, sign up for an account with each one and test them extensively to see how they function.