@Cameron Calvert I fear you are underestimating the gravity of the situation.

If it is an older gravity system there are not too many parts.

Pressure vs gravity. 

They still warrantied the foundation.Sewer lines are gravity fed, they never hold more pressure than the height of the water in the line.

you're asking hard questions my friend Appraisals work the same way gravity works: you'll kinda see a pattern, but no one really knows LOLYou must have good comps, but build in variance. 

Typical drainage through tried and true gravity is much more preferable me.

One thing my initial inspections came up with and really bugged me was an exposed pipe which had NO decline (it might even be defying gravity).Yes, whoever did this turned it into a disaster and yes, the contractor is in bankrupcy.

You can construct a gravity retaining wall fully on your property that keeps my property safe and does not take my property.

I compared a pump driven sewer connection and a gravity fed sewer connection.  

Water freezes in lower joints and causes joints to weaken, motar loss and weight with gravity plays on structures causing those stair step seperations.