A typical beer line cleaning kit costs about $50 (e.g., http://www.austinhomebrew.com/product_info.php?cPath=178_40_276&products_id=1209). The cleaning kit in this Instructable will cost just a few dollars.
Step 1: Parts Required
1. Soda bottle and cap. Use whatever size you need. I used a 2L bottle.
2. 1/4" vinyl tubing (whatever length you need)
3. 2 hose clamps
4. 1 locking air chuck
5. 1 hose barb adapter, 1/4" barb x 1/4" MIP
6. 1 1/4" barb to 1/2" MIP adapter (I used a nylon adapter from Lowes, A-193B)
7. 1 tire stem
A simpler and cheaper design would use a 1/2" male MIP to 1/4 MIP adapter in place the hose, clamps, and barbed adapters. I had all but the nylon adapter available, so that is how I made it. If someone tries the simpler design, comment and let us know how it worked.
Pour a beer before you start, as you will have to disconnect the beer line from the keg coupler in step 6.
Step 2: Assemble the Soda Bottle Cap and Tire Stem
Essentially, you drill a hole in the cap, and insert the tire stem. More details can be found here, at step 6 (thanks, letsapocalypso!): https://www.instructables.com/id/SBW6AS8F44XY5LY/
Step 3: Assemble the Cleaner
Attach the 2 adapters to the hose using the hose clamps. Screw the air chuck onto one end, using plumbers tape.
You should be ready for your second beer. If you are not used to using a screwdriver, you might be ready for your third. If you are Joe the Plumber, you were so fast that you will have to chug the first one.
Step 4: Fill the Bottle With Cleaning Solution
Fill the bottle with whatever beer line cleaning solution you use. I fill mine about 1/2 full (about 1 Liter).
Step 5: Pressurize the Bottle
Pressurize the bottle using CO2, an air compressor, or a bicycle pump. Use just enough pressure to push the cleaning solution through your lines. The simplest way to pressurize the bottle is with a bicycle pump. It will only take a few pumps. Caution: do not over pressurize your bottle. Have a professional pressure test your set up prior to use.
Step 6: Attach the Beer Line Cleaner to the Beer Line
After turning off your CO2 and removing the keg coupler from the keg, disconnect the beer line from the keg coupler. Attach the beer line to the 1/2" fitting of the beer line cleaner.
Before disconnecting the beer line, pour your third beer.
Step 7: Attach the Beer Line Cleaner to the Bottle
Attach the air chuck of the cleaner to the tire stem of the pressurized bottle.
Step 8: Invert the Bottle
Invert the bottle. You can hold the bottle, or prop it up, as shown in the picture.
Step 9: Flush the Line
Now, you can clean the beer line using whatever regimen you normally use, or as specified by your beer line cleaning solution. When you open the faucet, the solution in the pressurized bottle will flow through the lines, and out the faucet. After a little flowing, close the faucet, and let the solution sit in the line for 10 or 15 minutes. After pushing all of the solution through, rinse the line a few times with water. Watch out when the bottle empties, as the faucet will splash when the liquid is gone.
You may still may need to remove and clean your faucet using a brush, etc. You may also need to clean your keg coupler separately.
Step 10: Drink
Re-connect the beer line to the keg coupler. Drink massive quantities, and start thinking about how to design a big squirt gun using your fancy new beer line cleaner parts.