Step 2: Methods
1: Cut a hole in a box
Drill a hole in the lid of your fermentation vessel (or punch a hole in it, however you prefer to make holes). Make sure that it is very close in size to your nylon barb (or pen top). If you make the hole too big you risk not being able to make the seal airtight.
2: Put your junk in that box
Place your nylon barb into the hole you made in the fermentation vessel's lid (the barb should be on the external surface). I got a nylon barb from the hardware store for about $1.25. Lock it down by placing some hot glue around the hole and then quickly bolting the barb to your lid with its corresponding nut. If you are not satisfied with the seal, use more hot glue around the cracks where air may escape.
If you are doing the bare minimum method, put the tapered pen piece in the hole (tapered end facing outward) and tape it down like hell. I am assuming duct tape would be the tape of choice for this method.
3: Make her open the... I mean hook up your tubing
Hook up your plastic tubing. I bought mine from the hardware store for 18 cents a foot but I am sure there are plenty of places you can get it (Maybe some aquarium tubing from a pet store? Not pre-used though, that would be unsanitary). Either way, I bought 2 feet of tubing which worked out quite well, you may need more if you are not using a bucket as a fermentation vessel and have to set the jar somewhere farther away. As explained in the step's title, hook up the tubing to your barb (if using a pen tip you may want to using something, like tape, again to make sure your seal is still air tight, this problem is not as prominent in the barb method though).
4: Cut many holes in your jar's lid
Cut a main center hole in the jar's lid that is large enough for your plastic tubing to fit in, the size of this one is not that important. I place a little bit of tape around the rough edges of the hole as to not damage my plastic tubing. Also, poke many smaller holes around the center one to allow CO2 to escape from you airlock jar.
5: Place your tubing below the water level
This is pretty self explanatory, fill your jar about halfway with water and place the tube below the water level so that CO2 can escape from your vessel but will not come back in (due to the water barrier). I found that the closer the tube is to the water level (while still being below it) the quieter the bubbling noise is.