A built in overflow box is the most efficient method of draining aquarium water to a filter. If your aquarium does not have built-in overflow, CPR Continuous Siphon Overflows/Prefilters are the best means for getting water from an aquarium to a sump style filter system without expensive modifications to the tank.
The advantages of CPR Continuous Siphon Overflows/Pre-filters include:
Tip: Connecting the bleed hose from the overflow to the air intake of a power head will help the overflow continue to work if it draws some air into it. It will also help the overflow restart in the event of a power failure.