Your real estate people must be pretty clueless if they couldn't advise you on this. I'd be inclined not to buy anything through them. Are they city realtors who know nothing about the country, where the house is? Do they not know that there are cameras that can be sent down sewer lines to check them out? Guys who clean drains use them, plumbers use them, and the guy who checked out my septic field before I bought this house used one to inspect the system. I don't know what kind of "professional" that was.
The thing that "grinds sewage" sounds like it might be a treatment plant(I had one at my last house), in which case you probably have a septic field, but hey, I'm not there to see it so my opinion on that isn't worth much. I've never heard of anyone needing to treat sewage before it goes into a sewer but I guess it's possible.
Are there any neighbours? They might know something. And, if a sewer line is put in after houses are built, usually anyone along that line who has septic has to switch and hook up to the sewer line when it's put in. So if the people next door are on sewer, you probably are too.
If the health department knows nothing and you find a septic field, that would bother me. It means that the field is so old it was put in before permits were required, or it was put in without a permit. Relatives of mine are just coping with a similar situation. Their septic field was installed many many years ago, by the original owner, under the driveway and parking area, which is a big no-no. Now that it needs repair, that old field cannot be repaired because it's way outside any current codes. It's going to cost them around $25,000 to get a new field and a treatment plant to comply with code. The whole parking area, the side yard of the house and part of the front lawn are all going to be dug up and a tree had to come down to accommodate all this. I bet it'll cost even more in the end.
I sure hope you have the right conditions in your sale contract, ones that allow you to bail if the info about the sewage disposal is not available, because I'd be very uneasy if I was looking at this house.