There were several versions of the TapCap before I settled on this one. It is basically a modified Tee fitting. I mounted the fitting in the cap for a 3L soda bottle. This fitting can be mounted in a 2L cap as well. Construction is fairly straightforward and uses tools typically found in a handyman’s toolbox. The various brass components can be found at a hardware store.

Here's a drawing of the TapCap and a bill of materials:

Here are some photos of the TapCap and it's components:

You will also need: 1. vinyl tubing, 3/16 ID provides a tight fit 2. small hose clamp 3. cobra/thumb tap 4. bicycle tire inflator that uses either 12 or 16 gram CO2 cartridges

I used a tap to clean out the threads in the T-fitting so that all the other fittings could be inserted fully. The most important one is hole for the close nipple. The close nipple should be able to be inserted half way into the T-fitting. After all the pieces are fitted together, solder them in place. Use lead free solder and non-toxic flux. Don’t forget to remove the valve stem from the tank valve. The valve stem has some rubber and plastic seals that WILL melt. In order for the copper tubing to pass through this newly created fitting, you will need to drill out the compression fitting. A 1/4” drill bit will work but I found that using one size large allows the tubing to be inserted much easier. Leave about 1/2-3/4” of tubing sticking out the top of the compression fitting ferrule/nut and then tighten the compression nut. Drill a hole in the center of a soda bottle cap. Insert the grommet and the insert the assembled fitting. You will need to make a nut to secure the fitting in place. Cut the nut from item #8. You will probably need to tap the nut a little more so that it is able to tighten properly. Install the assembled TapCap on a soda bottle, if the copper tubing is too long, cut it to fit, if it is too short use a piece vinyl of tubing on the end of the copper tube to reach the bottom of the soda bottle ( I cut my tubing to fit a 2L bottle and use the additional vinyl tubing for the 3L bottles).

Attach the tap to the short piece of copper tubing at the top of the TapCap with a hose clamp. Use the bicycle inflator to provide pressure to dispense. A word of caution: make certain that the CO2 cartridges are for human consumption. Cartridges that are for air guns and other air actuated devices often include a small amount of oil for lubrication you don’t want this in your beer and you don’t want to drink it. I got my tire inflator at Essex Junction Bicycles. Several mail order places carry CO2 cartridges that are for dispensing purposes. I have found that a 12 gram cartridge will dispense nearly 6L of beer, the larger 16 gram cartridges should have no problem dispensing 6L .

Here's an air valve attached to a bottle cap for carbonating brews:

John's Bio:
John is Customer Service engineer for Applied Materials, a manufacturer of semiconductor equipment. A self professed gadgeteer, he can often be found in his workshop tinkering. Amateur radio and his Harley Davidson Sportster also occupy what little free time he has. John has been homebrewing for 5 years, he has recently begun all-grain brewing after 4 years brewing with extracts and specialty grains. John would like to acknowledge the graciousness of his wife, Judy, who indulged him and his hobbies. He can be contacted by e-mail at:john_e_schnupp@amat.com for additional information.