I think I have a good idea about how to go about this, but wanted to throw it out here to make sure I don't wander down the wrong path. I recently installed a new floor drain. I broke up the concrete in a circle around the old drain, maybe 14-18 inches in diameter. Under 2-3 inches of concrete was gravel and a few more inches down was the clay dirt under the house. Below is a picture generally representing this. There was a 4" PVC pipe running up from the ground where the old drain was attached. I cut off the old drain and solvent welded the new drain (also PVC) onto the end of the pipe. Now I want to fill the hole back in and finish the concrete level with the new drain.
I have a pile of gravel, broken up concrete chunks and dirt which I excavated from the hole to access the pipe. I could put some of this material back in, maybe fill in around it with sand, building up layers of that until I'm about where the concrete begins in the surrounding slab, and then fill that area in with concrete. Does this sound about right? Am I way off?
Also, I welcome any suggestions on what kind of concrete to use (or what to specifically avoid). Once it's dry, I'll be grinding the surface of it (and the entire floor) in order to lay down a sealer or epoxy or something.