We have accidentally flipped a few places and thought "hmmm... well, maybe since gravity is pulling us in this direction, maybe we should just go with the flow?"

I had a sewer inspection to confirm the gravity of the issue ($7000 sewer job awaited us) and negotiated back down.

Plus, just like @Jamie Rose said, as long as you can open a window it's very rare to get too hot for people.I haven't yet closed on my first property, so maybe my opinion doesn't have a whole lot of gravity.

I have found them to be useful with the expectations that they're definitely going to find problems, it is a matter of the gravity of those issues and how you plan to handle them. 

If you have a simple gravity system, how old is it and how often has it been pumped? 

But rather, since water seeks the path of least resistance and is subject to the laws of gravity, it will naturally collect in low spots.I was just on a project this year in which, despite having a floor drain, the concrete was not sloped properly to it and so water puddled elsewhere in the low spots of the basement.

I ran it for several years prior to that with window units & old gravity Oil Furnaces (what a PITA they were).

Why would you put a back flow preventer on a gravity flow system?

Hey small park like that is probably a standard gravity fed system. 

Most did not understand the full gravity of the home loan and buying process and due to that I had to redo a lot of the work myself since the departments in NACA do not have efficient systems of communication.