How to cut a hole in a concrete floor slab

I have a septic tank that I'll need to have cleaned sometime in the next 6-12 months as a prerequisite to selling our house.

Before we bought the house, the tank was under the dirt floor of the outdoor carport next to the original house. The "genius" who owned it remodeled the house several years before we bought it, and poured a concrete slab completely over the entire dirt floor of the carport and turned it into part of a new interior addition to the house. So now the septic tank opening is somewhere beneath the carpet in our home office! Not to mention somewhere beneath the concrete floor beneath the carpet! :furious:

I knew this when I bought the house. When I pull back the carpet, I can see where the "genius" either jackhammered or sledge hammered a hole to get at the tank opening, and then repoured concrete to fill the hole when he was done.

I want to do it in a better more repeatable fashion. I want to cut a fairly neat hole in the slab, and before I fill it, I want to have a local welder fashion some sort of metal frame I can insert and mount inside my opening in the slab, and then lay a metal plate (I'm thinking plain steel about 1/4" thick will be fine) inside the frame, so that the next guy doesn't have to do what I'll have to do this time! :furious:

So here's my question: what sort of tools or techniques are there for cutting this kind of hole? The part of the slab where I need to do this is in a small alcove in the office, not in the middle of the room. So I don't have room, I think, for those massive diamond bladed concrete saws you drive by on the endless summer concrete roadwork repair jobs. And I can't imagine a huge air compressor-powered jackhammer tearing up my house! What else is there, other than hiring some hulk to just bash the crap out of it with a sledge hammer? :huh: