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.

Each person has a different method of drilling glass tanks. 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. Drilling glass comes with its risks. We recommend that you wear safety equipment and that we are not held responsible for any injuries, loss, or damages that may occur during the DIY project. According to our experience, thicker glass is more likely to crack. Aquariums with a volume less than 40gallons are made of thinner glass. They tend to break between 10-25% of all cases.

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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Some aquariums have tempered glass in the bottom, but they use non-tempered for the side walls. Place a cell phone or laptop inside the tank to check if its side walls are made from non-tempered glass. 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 has been tempered, the screen will show splotches and stripes when the sunglasses rotate. This effect can be seen online in video examples.

Instructions for Drilling Aquariums

1. Place the aquarium so that the tank wall will face upwards. Place the piece of wooden against the tank’s side edge. 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. Mark the wood to indicate which side is touching the rim.

1. You will need to take the wood from the tank. Drill a hole through the wood where the dot was. You should prefer to use a hole saw designed for wood. The diamond-tipped holesaw will work, but it may cause some smoke. The guide is now used to make sure the hole saw doesn’t move when drilling. 2. Once you have created the guide, place the wood piece against the tank’s side edge and rim again. Tape the aquarium inside where you see the hole. This will ensure that it doesn’t fall out and cause damage to your tank when drilling the glass hole. The tape also helps reduce chipping so that the hole is fairly clean.

1. Fill the hole of the guide with water. You will have to refill the hole with water as some of the water may leak out. Water is useful to clean away dust and keep the holesaw from getting too hot.

1. The electric drill will spin slowly if you squeeze the trigger. Gradually increase the speed until it is spinning at a slower pace. You should apply a light pressure on the holesaw, allowing the drill to move downwards. The hole saw should be kept level. Do not tilt the drill to make the hole uneven. 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.

1. Pour more water into the guide and onto the hole saw if the glass is making a loud squealing noise. Then continue drilling. 2. When frequency of the grinding sound starts to change, the glass hole is about to or has already broken through. Although there may be some edges that are slightly jagged, the bulkhead’s gasket will completely cover them. Do not touch the glass hole’s interior.

Diagram for bulkhead fitting

1. The bulkhead is quite fragile so make sure to place the aquarium in its final position before you attach the bulkhead. Place the bulkhead into the hole. Make sure the gasket, flanged head, and locking nut are facing the outside of the tank. Continue tightening the locking nut using your fingers, and then cinch it down with pliers.

Congratulations on drilling the first aquarium! A final tip: make sure to use high-quality hole saws, and that they are replaced regularly. Our hole saws can drill approximately 8-10 tanks before they start to wear out. 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. Stock up on the bulkhead fittings we use in our home aquariums and fish store.