The beer line of a draft system is the plastic tube that carries the beer from the keg it is stored in to the tap that dispenses it. The various components of any beer leave behind traces of residue and sediment in the beer line, which build up over time. After two weeks or half a keg's worth of beer, your line will need to be cleaned out. Diligent maintenance of your line will keep your beer tasting fresh, pint after pint.
Turn off the carbon dioxide and regulator by rotating the knobs on the valves all the way to the right.
Unscrew the coupler from the top of the keg. Pull the beer line off the regulator so you can clean it.
Loosen the tap using the tap wrench and set it aside. Screw the outlet on the pressure pump sprayer onto the tap valve and tighten the nut to hold it in place.
Twist the liquid canister off the pump sprayer and fill it with water and a capful of cleaning solution. Replace the canister on the sprayer.
Place the beer line into a large bucket and start pumping the pressure sprayer fluid through the line. The fluid and dirt in the beer line will come out the end of the line and into the bucket.
Refill the liquid canister with plain water and run it all through the line. Keep pumping the liquid until the line is releasing clean water.
Disconnect the pump sprayer form the tap with the wrench and reconnect the tap. Reattach the beer line to the coupler.
Screw the coupler back onto the keg and turn the carbon dioxide valve all the way back to open. Open the regulator valve once the CO2 is open.
You should clean the tap once you have it removed from the lines anyway to keep your beer really clean and crisp.
Do not change a keg without cleaning the lines as well.