Fill any cracks first with cement or vinyl patch.

My plan is to install the cement board directly to the studs.  

If the school is on a slab you're going to have a difficult time cutting in plumbing (literally cutting it in through the cement slab). 

I would camera that line to the street quick,,,sounds like the least little thing is finishing the plug up and everything is backing into the washer drain since its the lowest.Since the trap is above cement try replacing that part with 2" plastic,,put a cleanout wye past the trap and have easier access to clean itAND they would get an addendum to the lease post haste,,,any more grapes,tampons, cig butts,toothpicks,,,ANYTHING besides water and waste gets them a bill for time and materials,,,and make it STICK!!!

We had a handshake between the seller, Wally, and the buyer, me, cemented by a purchase offer signed by the three of us.

Tonight a neighbor showed us video footage of our tenants daughter defacing the cement. 

He recommended "cleaning the main sewer, chiseling out cement, to remove vent plate for access into main".

The aspalt idea is not bad, I just thought about doing it with cement but I like that better.

I find it attractive, but consider the cost of the cement board you would have to install as a subfloor because it is upstairs and not on a slab.

Just opening the slab and removing the old cement can easily take 2 workers a half a day easy it's not like new construction where everything is open and exposed.