I'd say try it. Thats how jc1119 installed his. I didnt like having all the flow run through a 3/4 inch fitting so i drilled it. Im sure jc's method works fine. I jist didnt see myelf going through the hassle of actually cleaning the foam inside the boxThat would save a few bucks and a some time drilling the sides of the boxes. You would just use the screw on "grate" piece instead so nothing is sucked up by the impeller