This brief instructable shows you how to make a quick and easy adapter to allow you secondary your beer in-keg so you can go right to drinking it once the secondary fermentation is complete. Not only does this eliminate another transfer it also allows you to eliminate glass carboys from your brewing milieu which can be dangerous if they shatter at the wrong moment.
Step 1: Parts
This is a pretty simple project, using parts I had on hand. A little google searching shows that this isn't a new idea, and that many other folks have come up with a similar idea. Great minds... Some of these used threaded fittings, simple hoses as a blow off or other variations on the same theme. Anyway, to complete the project as pictured you'll need the following
Gas-in fitting for keg
Plastic bubbler airlock
Epoxy, preferably marine grade
Torch or heat gun
I'm using a ball-lock style keg and a barb type rather than threaded fitting as pictured. I had a really crappy plastic bubbler airlock on hand that wasn't good for much so I used that. Since this assembly is going to be in the presence of moisture, I used a marine grade epoxy to prevent long term weakening of the bond. The heat source is needed to make the bubbler flexible so you can bend it and form it. I used a sweet little torch from our friends at DX. This thing has a million uses, soldering, brazing, blazing :), de-icing locks, cauterizing, sanitizing, etc. So if you don't have one, buy one.
Step 2: Make It
Making this project is pretty straight forward. I don't have intermediate photos showing each step, but you can get the idea. Basically all you do is use the torch to gently heat the end of the bubbler, push the end fitting of the keg adapter into the tube of the bubbler so the bubbler tube expands to fit over the keg adapter. Depending on your fittings and bubbler this may or may not be required. Once you're sure your bubbler will fit over the keg adapter you can use the torch to gently heat the plastic tube of the bubbler so you can bend it so that it sits upright when installed on the keg. Perfectly upright is not required, but you want to make sure that air can't bypass your water airlock when in use. Be careful not to blow a hole in your tubing or kink it when heating and bending. If you do, fix it with epoxy.
Once the bubbler is ready to go, mix up some epoxy and apply it to the keg adapter barb, slide the bubbler on, and then goop epoxy over everything to ensure an air tight seal. Let it cure and you are finished.
With the epoxy cured, you can place this assembly in the gas-in side of the Cornelius keg and add water to the bubbler and it will function as an airlock for fermentation. I've only used this for secondary, where not a lot of trub or activity takes place since the kegs get filled pretty close to the top and I don't transfer (rack) the secondaried beer off of whatever settles out. If you don't rack off, not that there is anything wrong with it, then the first few pours from the keg will be yeasty or otherwise filled with the crud that settled out so don't plan on drinking them. No big deal. I've used this setup to dry hop during secondary as well. Just place a hop bag full of your hops in the keg when transferring from primary to secondary and leave the bag in there until you drink all the beer and are cleaning the keg.
If you leave enough head room in the keg to allow for krausen you could theoretically use a keg and this airlock to do primary fermentation as well. However primary is messy and I don't like scrubbing kegs and tubes and fittings. I use a big plastic buckets with a food grade plastic liner (trash bag) which lets me transfer the beer out of the bucket, pull the bag full of yeast and crud out, and dispose.