In most cases you don't need to glue the PVC to the rack depending on frag tank size and how tall you want the rack from the set face make sure you cut the PVC to size put in all 4 corners if a large piece put one in dead center use if you can 2-2.5" PVC for max stability and no wobble. If and if you want to do so drill straight threw the PVC and put a zip tie to ensure maximum stability. But that's just a option don't have to do so. We just sit the rack on the PVC.