Materials needed: 

• Vivarium or Glass you plan to drill
• Diamond Hole Drill Bit
• Putty of some kind (Plumbers putty)
• Carbide Powder (optional)
• Electric Hand Drill
• Plastic disposable cup
• Gloves/Eyeglasses
• Bulkhead

There are many purposes of drilling a hole in your vivarium glass but mostly it is to install a plastic "bulkhead" that will allow for a pipe or hose to be attached to the glass and not leak. This hose can run water to and from pumps, sumps, canister filters, or just be a drain to prevent oversaturation of the vivarium soil. 

Whatever the case, drilling the glass and installing the proper size bulkhead is the proper and leakproof method. 

Getting the proper size bulkhead and associated proper size diamond bit drill is key. I personally mostly use 1/4" x 1/4" threaded bulkheads for most of my vivarium builds. A chart below will show the proper size bulkhead to diamond drill tip diameter. If in doubt you get a set of the bits, or you might even find a matched set of bulkheads to bits. It used to be you needed to go to specialty stores for these but now you can find them on Amazon or ebay for cheap.

Placement of the drilled hole and bulkhead is a key aspect of all of this but it's outside of this tutorial.

 But if possible I try to place it above the waterline so it is less likely to leak, unless it is a drain line or is a filter intake line. 

To start, the best way I found is to have the tank on it's back or oriented such that the drilled surface is facing up. This is so that when you make a curricular dam of putty around the drill location, the putty dam will hold water. Do this first.

After making the putty dam, fill it with water and optionally add in carbide powder into the water. A teaspoon is plenty.

Using the diamond tip drill bit on your drill, begin to spin the bit slowly against the glass at a slightly angle while holding the drill as steady and still as possible. This will be loud. It will try to 'walk' on you. Hold it tight and still and try to get an initial groove started.

After the initial groove in the glass is formed you can begin to move your drill bit to be more flat against the glass and it will be much less likely to move or jump as it will be inside a groove. Then you can slowly increase the speed and pressure. It will be loud. It will take about 2-10 minutes depending on how fast the bit spins, the thickness of the glass and the amount of pressure you apply to the glass.

When you are close to drilling all of the way through your glass, place the disposable cup under the glass hole to keep the mess down. When the water begins to leak from the glass hole it will be dirty and having it drip into a disposable cup is a good idea.  The water will have microscopic glass bits so I use a disposable cup and just throw it all away and clean up anything left with lots of water and paper towels.

Install the bulkhead into the glass by putting the rubber washer on the inside of the vivarium and the plastic nut on the outside. You can now install various plumbing by screwing onto it barb fittings and pvc tubing. Be sure to use a sealing tape and/or sealing paste to make sure you don't get leaks.