Now you can drill out your tank with confidence. No more ruining your tanks trying to drill them when the drill bit moves. Make a perfect hole using our included template. Simply tape fast to your tank and drill. Included is a 1.75" diamond coated hole saw drill bit, the template, and (2) 1" slip x thread bulkhead. This can be used with or without a overflow box/surface skimmer to hide unsightly plumbing in your reef tank with a internal overflow box.