I digging a hole for a bathroom in basement how deep should the hole specs be for a in floor injector

I would suggest getting the sewer ejector pit and dig accordingly. If you don't have the pit but want to dig the hole now, I would suggest 30" wide by 36" deep. This should be big enough to fit any residential pit.

You say "injector" are you talking about an "ejector" pit or a pump up toilet. That sits on an elevated base or over a small pit.