A built-in overflow 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 filter system without expensive modifications to the tank. They quietly skim up to six times more water than units with tubes.
The advantages of CPR Continuous Siphon Overflows/Prefilters include:
-Adjustable water level allows you to easily change the level in your tank.
-Black top reduces algae growth.
-Quiet operation.
-CS Overflows now feature a grated inlet instead of the fish screen previously included.
http://www.marinedepot.com/CPR_CS_Overflow_Boxes_External_Overflow_Boxes_for_Aquariums-CPR-CR1511-FIOFEB-vi.html
