Now, if you take that money and used it as 20% down on a rental, the cash flow would have to cover two mortgages to break even. 

There are many other investors who would buy properties that would break even with one unit not generating income all day long in that area, and they'd offer cash and more than you appear to currently willing to offer.

@Cory H. another resource would be the county or state level body that governs the installation, use, and service of waste water treatment plants. 

You should be able to run it out for whatever period you'd like, at whatever interest rate and get a month by month break-out of total payment, the principal portion and the interest portion.  

At this point, I will likely just break even as the properties do not appreciate much.

do i take a loss of 14.5k per year or try to break even in a year or two, i'm not sure... 

A smart investor is not going to wait until all h*** breaks loose before trying to secure this type of loan (especially considering it takes months to get approved).

Kitchens/Bathrooms can make or break a home

Seller financed deal at $40,000 bathroom was down to studs, kitchen had no flooring and cabinets were falling off at the hinges, no gutters on rear of home, rear entry door suffered a break in and roof was leaking prior.

That basically breaks even with the 5% needed for a conventional.