How to Drill a Hole in a Glass Aquarium the Easy Way

While most fish keepers start off with easy, off-the-shelf filters from the pet store, some hobbyists want to take their aquarium filtration to the next level. By drilling a hole near the top of a fish tank and adding a bulkhead (i.e., waterproof plastic fitting that prevents the hole from leaking), aquarium water can be directly plumbed out of the tank and into a custom filtration system — like an aquarium sump, canister filter, or automatic water change system.

Everyone has a slightly different way to drill glass tanks — such as the usage of a drill press, mineral oil, dish soap, drilling from both sides of the glass, and more. We have drilled hundreds of aquariums for our fish store and personal fish rooms, so we've experimented with all of these methods. This article explains the tried-and-true technique we eventually landed on. That being said, drilling glass has its risks. We recommend wearing proper safety equipment, and we are not liable for any injuries, losses, or damages you may experience while undergoing this DIY project. In our experience, the thicker the glass, the less likely the tank will crack. Aquariums smaller than 40 gallons have thinner glass and tend to break 10–25% of the time.

Materials for Drilling Aquariums

• Glass aquarium that is not tempered
• Bulkhead (slip x slip)
• Diamond-tipped hole saw that matches the size of the bulkhead
• Electric drill
• Clamp
• Pitcher or bottle of water
• Flat piece of wood that is about 1-inch thick
• Sharpie marker or pen
• Painter’s tape
• Pliers
• Safety glasses
• Safety gloves

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While some aquariums have tempered glass on the bottom panel, they usually use non-tempered glass for the side walls. To test if the side walls are made of non-tempered glass, place a laptop or cell phone inside the tank so you can see its screen through the pane of glass that will be drilled. Make sure the device shows a white screen. Look at the device screen while holding a pair of polarized sunglasses in your hands and then rotate the sunglasses as if turning a steering wheel. If the glass is not tempered, the screen will look like it is shifting from white to solid black as you rotate the sunglasses. If the glass is tempered, stripes or splotches will appear on the screen when the sunglasses are rotated. Look online to see video examples that demonstrate this effect.

Instructions for Drilling Aquariums

1. Place the aquarium on its side so that the tank wall that will be drilled is facing upwards. Line up the piece of wood against the side edge and the rim of the tank. Position the hole saw where you want the bulkhead to be and draw a dot in the center of the hole. The hole should be low enough so that (a) the overflow or drain is at the surface of the water and (b) the locking nut of the bulkhead won’t hit the rim while tightening it. Also, mark the wood so you know which side of the wood is touching the rim.

2. Take the wood off the tank and drill a hole in the wood where you marked the dot. (Ideally, you should use another hole saw that is meant for wood. If you decide to use the diamond-tipped hole saw, it will do the job but the wood may smoke a bit.) The wood now serves as a guide so that the hole saw will not move while drilling.
3. After the guide is made, line up the piece of wood against the side edge and the rim of the tank again and clamp it down. Tape the inside of the aquarium where you see the hole so that when the glass hole is drilled, it will not fall out and crack your tank. The tape also helps reduce chipping so that the hole is fairly clean.

4. Fill the hole of the guide with water. Some of the water will leak out so you will need to keep refilling it to keep the glass sufficiently wet. Water helps to wash away the dust and keep the hole saw from overheating.

5. Squeeze the trigger on the electric drill so that it spins at a slow pace and gradually increase the speed to a moderate pace. Apply a light, even pressure on the hole saw, and let the weight of the drill to carry it downward. Plus, try to keep the hole saw completely level and do not let the drill tilt or else the hole may get cut unevenly. The goal is to slowly file your way through the glass, so the drilling step may take up to 5–20 minutes, depending on the thickness of your tank.

6. If the glass starts making a squealing sound, pour more water on the hole saw and into the hole in the guide. Then continue drilling.
7. When frequency of the grinding sound starts to change, the glass hole is about to or has already broken through. There may be some slightly jagged edges on the hole, but the bulkhead’s gasket will cover them so no need to deburr the hole. Carefully pull off the tape, and do not touch the inside of the glass hole.

Diagram of bulkhead fitting

8. The hole is somewhat fragile, so place the aquarium in its final location before installing the bulkhead. Insert the bulkhead through the hole so the flanged head and gasket are on the inside of the tank and the locking nut is on the outside. Tighten the locking nut with your fingers and then finish cinching it down with pliers.

Congratulations on drilling your first aquarium! As a final note, make sure to use good quality hole saws and replace them often. The hole saws we bought can drill about 8–10 tanks before they wear down too much. The longer you use your hole saw, the more likely the aquarium will break while drilling. If you plan on drilling many tanks, get a pack of multiple hole saws and save yourself the headache. Also, stock up on our favorite bulkhead fittings that we personally use in our fish store and home aquariums.