the water is sucked thru it, i use those in my HOT mags on each tank. since its end of summer you can pick up the same type of cart at most mass retailers look for 'intex' pool carts if you want to add a power head on top of it. they come in different sizes and are very cheap to play around with DIY ideas. these type of filter carts are not for long term constant filtering since they clog up fast and need to be changed/cleaned, often for a power head filter open cell foam would be more ideal