Drilling holes in your glass aquarium tank can be daunting but it can also save you the hassle of hauling your tank to a shop. Bulkreefsupply.com carries Diamond Coated Glass Drill bits so that you can do this at home. The bits come in sizes ranging from 30mm to 85mm and should fit the Schedule 80 or ABS bulkhead you are using. Use the Glass Drill Bit Guide or the Drill Press Attachment to help make this process easier.