I'm thinking personal loan. The property is "grandfathered", this the outhouse. Not sure what that means exactly, as far as a new owner.
You will probably find that "grandfathering" only applies to the status of the house with respect to what the county or governing body (municipality) requires for waste disposal. A pre-existing outhouse could be grandfathered, meaning the addition of a septic system would not be forced on you. This type of grandfathering tends to be married to the structure, regardless of owners, so as long as the house is standing and livable you will probably be able to use the outhouse. Where is the sink water going at the moment, out on the ground?
However, this grandfathering does not extend to how a bank will feel about that asset. Expect banks to balk as soon as they realize there is no formal waste disposal system. You probably will not be able to add any additional plumbing without the addition of a septic system, or hooking to town sewer because new plumbing will have to adhere to current health department standards.
If the property really is that perfect for you, you may be able to take advantage of the fact that the seller's pool of buyers will be extremely small to negotiate a great deal. This is a fairly risky proposition though, especially if you live in an area where septic rules have become strict enough that some properties just won't accommodate a septic system any longer. In some places, where a traditional septic system won't work, but there is an existing structure, the law allows for the use of experimental septic systems like a peet moss system. You would really need to do some digging on what your local governing body allows. If you have sewer access, that would make things much less risky, because while it would cost you a healthy chunk of money to hook up, there's probably no chance you could be stuck with a property that has no waste disposal options.
You absolutely need to verify all these things with the governing body that applies. While this is a potentially risky property, under the right set of circumstances (waste disposal access is known, seller is willing to negotiate extensively to sell, etc.) it could be a pretty sweet deal if it's exactly what you're looking for.