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

Window ACs are designed to hang downward toward the back of the unit, so gravity will pull the condensation out of the back drain which results in the water dripping outside the house. 

So I have an old gravity heater and am looking to get it replaced.

It's looking tired inside and has knob and tube wiring, asbestos lined heat ducts (gravity heat), original plumbing, it needs a new roof and windows soon and some siding work and a paint job.

You probably have a straight gravity system so maybe get some different people out for estimates. 

Just getting a gravity sewer line to a property often costs more than the land so you need multiple lots to even begin to make it pay.BTW most governing bodies frown on septic systems for new development.If you have a particular plot of land in mind send me a pm and we can discuss particulars.

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

Depending on what the actual problem is, the repair would likely involve cutting a foundation drain (a gravity drain on the interior of the foundation wall) which may also require a sump pump if it's below grade.

Would you "fudge" the rules of gravity when putting together schematics for a plane?

Brings back memories of the good old days of their gravity defying adventures.