Drilling a Glass Tank By … Nay,kid and lReef lKeeper This article is ONE of very many ways to drill a glass tank. It has worked for us well over 500 times with 0 tank breaks so far (you never know … it could happen). If you decide to try this at home, we can in no way be held responsible for damages to your tank(s), YOU ARE DOING THIS AT YOUR OWN RISK. 1)Do the research … make sure and be 100% positive that your tank is NOT TEMPERED. Most tanks under 75 gallons are NOT tempered on the bottom, but you are drilling this, so unless you want to buy a new tank … MAKE SURE it is not. Most tank suppliers put a sticker on the bottom of tanks that are tempered, but the sticker could have come off or have been removed. Most larger tanks are not tempered on the front, back, or sides, but it is still up to you to make sure it is possible to drill the tank in the first place. 2)Plan the phases of the process well. You will have to figure out where the hole’s are going to be drilled, match the drill bit to the bulkhead. The bit needs to be as big as the OUTSIDE diameter of the bulkhead, carefully measure each hole, and mark the hole with the bulkhead (the center of the hole should be in the center of the bulkhead. We trace the outside of bulkhead for a perfect circle on the tank. 
3)We use clay to create a dam type structure around the hole. The dam is about 3” tall and about ½” bigger than the hole you are drilling. Be sure that you press the clay firmly into place and that the inside of the dam is stuck to the glass creating a leak free barrier. You will also want to place a catch container inside the tank, under the spot where the hole will be drilled to catch the plug of glass that will fall when the drill breaks though the tank. Fill the dam ½ to 2/3 of the way to the top with water. This will help keep the glass and bit cool while drilling.
4)Set the clutch on the drill low, so that when the drill breaks though it stops spinning the bit. Sometimes as you break through the glass the bit catches and the clutch set low will keep it from damaging the tank or the drill.
5)Stabilize yourself so that there is no movement in your body or the tank while you are drilling. We do this by bending the knees and bracing them against the corners of the tank. Start the drill at a 45° angle to keep the bit from roaming around in the dam and to get a clean start on the hole. As you feel the bit beginning to make a grove in the glass, slowly bring the drill to a vertical position on the glass. Slowly work the drill around in a circular motion to create the perimeter of the hole that you are drilling. Once you have the groove all the way around the hole, go perfectly vertical on the rest of the hole. You will want to lightly pump the drill up and down every 10-15 seconds to allow the water in the dam to flush the glass dust out of the groove. Remember that you are not so much “drilling” a hole as you are “grinding” the hole.
It does not take a lot of pressure to drill the hole. Let the weight of the drill do the work. Do not press on the drill, the bit and weight of the drill will be plenty of pressure to do this. As you see the water start to drain through the tank lighting up the pressure considerably on the drill. If it takes 10 minutes to drill the hole … 8 of those minutes should be on the part after the water starts to leak through the tank.
You will want to have someone there to help you. You will need them to add water to the end of the process as the water will leak from the hole that you just made and the glass and bit will both still need to be kept cool. There WILL be a small chip or two on the inside of glass, but the bulkhead covers them and they will not hurt the integrity of the tank.
6)Take you time … go slow … and good luck. We hope this article helps.
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