and civil engineers .. it sounds like the property is unzoned.. which I am not clear what that means in Texas.. from gossip of old I took that to mean you could do anything you wanted that could be physically built.. biggest issues for development of say housing.. would be water  sewer electric and storm drains if necessary.. so you could start at the county... 

Get it drained and contained as much as possible so it doesn't get worse.

I've seen older properties with 1-1/2" drains and older high-volume showerheads that have overwhelmed the drain's ability to compensate.  

Find out what service providers the “big guys” are using.For the big ticket services, I like to price compare a few common service issues BEFORE something happens.For example;Plumber: Replace a 50 gallon water heater (or whatever size you have) normal and after hour pricing, in case it goes out on a weekendSnake / clear a clogged toilet ( I have a photo album of all of the things our plumber has found in clogged drains over the years ) don’t judge!

Appreciate the advice to a newbie.a) Do you guys give the tenants drain cleaners or something like that to put once a month to prevent plumbing issues.

One of the properties I manage had a rusted out drain pan and the warranty didn't cover it.

The tank is right there under the sink so draining will be a cinch.

We also outline more specifics in our property rules (decorating, landscaping, arials/antennae/cable/dish, HVAC, pest management, drain stoppages, winterizing, etc).

Plumber said the wax ring was fine, but that he needs to bring in the longer auger to see where there's a clog in the drain.

They all have similar issues:Knob and tube electrical, old cast iron plumbing stack that may or may not need replacement, lead drain pipes in the 2nd floor bathrooms, along with the standard ugly/old kitchens, bathrooms, and seriously needing some new paint.The big things you need to look out for:* the main sewer from the house to the road.