What is the best way to fill a hole in a concrete basement floor?
Let's not over complicate this little project.  I have seen these open sump holes hundreds of times. I am absolutely sure there are no structural issues here, how long has the house stood without concrete in the hole? There was probably not a concrete floor when it was built and for many years after.  If you want to simply keep stuff out and hide the dirt then let's do it simple.  Dig out to about a total of 4 inches below your water pipe and valve. Mix up a small bag of  Sacrete concrete mix and fill the hole to about 1 inch under the pipe. Float it smooth, you're done.  There is no need to get carried away with a special base etc. The size and weight of the concrete patch is negligible as far as settling or shrinking is concerned. Get the stuff and be done with it in an hour!