From my understanding of AZ law, the landlord is required to keep the property sanitary and clean (like with water supply, drainage, ventilation, appliances functioning, no mold, etc.). 

Basic back of napkin calc using 70% rule has the purchase price too high

The current favored approach is two capped pipes, each with a sanitary tee into the main line.

Phila has a single sewer system in the older area where both storm water and sanitary waste water feed into.

My lease...Tenant shall refrain from disposing of things such as diapers, baby wipes, sanitary napkins, tampons, paper towels, wads of toilet paper, newspaper, children’s toys, matches, Q-tips, balls of hair, grease, oil, table scraps, clothing, rags, sand, dirt, or rocks into drains or toilet.

The 70% rule you are quoting is ONLY a quick back of the napkin equation and NOT really a rule.

Sounds like you need a property manager that will actually enforce the part of your lease that says Tennant's must keep the unit in sanitary condition, I think if you were going to be able to train these guys about how to treat your house you already would have.

I really dislike particle board especially the sink base cabinet.One leak and they swell up, crumble and it's irreversible.Tenants always put too much stuff into their sink cabinet.  200 bottles of hand detergent, DW detergent, cleaners, bleach, comet, rolls of kitchen napkins, candles, extra kettles, and 500 supermaket plastic bags filling every air void existing in there meaning any minor leak will not be noticed by them until it's pooling on the floor.

I'm sure this Old Dog keeps track of everything on a napkin.  

We originally signed a back of the napkin agreement with one another for 2 years.