I bought the filter mentioned above and when I was putting it in I noticed holes in the back where the clip for the motor are. Does this mean that the water is being pulled from there instead of the sponges?
yes it is pulled in from both front and back
I have the stingray 15 and for small tanks they are good filters but take up some room.
the good thing is they can be positioned on the bottom of bare tanks(ie. no substrate) ideal for fry set ups, providing the fry are not too small of course.