However, she is a bit of a pro and may try and drain me which makes me think sticking to the eviction process will be my best bet.

Theres a separate 2 car garage with a concrete floor with drain the owner uses to detail boats.

Still need to put the drain tube in. 

I'd be interested to know where the drain/waste/vent stack from the 2nd floor comes down to.

One of the lessons I learned on this house was to make sure your shower/bath drains are capped before they demo them.

The two kitchen sinks are connected by a T-shape drain pipe. 

I had one licensed contractor pour concrete down a drain. 

You can even split that into multiple properties if the cashflow numbers make sense.On the smaller factors side - $300 HOA IMO is down the drain which is one of the reasons I like to avoid Condos.

Had a sewer company snake out line at my rental home.  2 weeks later drains backed up again and had another company look at it.  

This also includes level above the water table if there is no municipal sewer system available, the lot must be high enough above the water table so the septic system can flow downhill from the house to the tank to the drain field.