Creative Financing for new Septic System

[Austin Keelen]

We have a home under contract in NJ and the inspection revealed that the home has a modified cesspool that needs to be replaced. Sadly the home is not close enough to a sewage line for that option so a new Septic Tank is required. 

We sent the requirement as well as a list of other repairs back to the seller (who is a lawyer acting as the executor of an estate) and they came back with taking 15k off the price if we accepted it as is. 

From my research it appears as though 15k may just barely cover the cost of the new system because the new system first needs to be designed by an engineer and then it can be priced. 

Also, I don't want to throw 15k straight into the house before I can even live in it, we have that money but it would drain me almost completely after the down payment.

Has anyone figured out a way to finance a septic system back into the mortgage some how? Or have the seller pay for it some way? 

Any help would be greatly appreciated, this home is stressing me out and we don't even own it yet.