How does an overflow work?

[true perc]

How does an overflow work?
Is it when u have a pump running from ur aquarium to a tank underneath yours or beside filled with bioballs or algae and then pumped back in to a box and then the water overflows out of the box into your aquarium? If so how much does it cost (Canadian)?

 

[ekclark]

An overflow consists of a U tube which runs a continual syphon out of your tank into a box which has tubes going to a remote sump. The sump then has a pump in it that moves the water into another tube back to your tank.
There is an overflow box that hangs inside of you tank to keep the U tube from sucking up large objects or from taking in too much water if your pump dies. It is really much more simple than it sounds.

 

[steven's un]

go to all-glass.com ........they have a good description of how it works...i have one and the drilled tank cost about $50 more and the overflow accessory kit cost about $42

 

[broomer5]

There are internal overflows ( drilled tanks ) and external overflows that hang on the back of a tank.
Here's info on external ones.
External Overflows