[mr_alberta]

You have a hole drilled in your tank so water drains from the display to the sump. Then you have a pump pushing water from the sump back into the display. This is what gives you your flow rather than powerheads.

You could also have a hole drilled in your tank and run a "closed loop" where water is sucked through the hole and pumped directly back into the main tank without going through a sump.