Make an Airlock for Wine and Beer Production

An airlock lets carbon dioxide (CO2) escape from fermenting wine and beer without letting outside air in.

Steps

Clean out a clear plastic bottle. Prescription pill bottles with the label removed work well.
Drill an {{safesubst:#invoke:convert|convert}} hole in the lid and a hole the size of an average ballpoint pen in the bottom of the bottle.
Take the guts out of a ballpoint pen so that you have an open tube remaining. Insert the pen in the bottom hole of the pill bottle and push it in all but {{safesubst:#invoke:convert|convert}} from the top. Mix fast-curing two-part epoxy and seal the pen to the bottle.
Clean out a rifle cartridge (30/30, 7.62, or anything with a diameter greater than that of the pen). Place it over the end of the pen inside of the pill bottle.
Drill a hole in a cork slightly smaller than the diameter of the pen. Place the end of the pen all the way through the cork.
Fill the pill bottle with water up to {{safesubst:#invoke:convert|convert}} below the top of the pen inside.
Insert the cork end into the bottle in which you are fermenting your wine, beer, or moonshine mash.

The airlock works on the exact same principle that your bathroom sink does for the trap below the basin. It creates a pocket of air that can escape through the top, but doesn't allow air from above to enter. You can substitute any of these parts with similar items. Clear plastic bottles are easy to work with and it's important to see the bubbles in the water to know that your solution is fermenting properly. The CO2 goes up the pen and is then redirected below the water by flowing down the rifle cartridge and out the top of the pill bottle through the hole you drilled in the lid. A commercial airlock will do exactly the same thing and will cost you 10 to 20 dollars. With 10 minutes of work, you can make this for pennies.

Be sure to let the epoxy cure for an hour before filling with water.
Check the water level in the airlock every few days to make sure it's high enough, as it evaporates slowly during this process. The bigger the pill bottle you use, the less you'll be adding water.