In earlier articles, I've mentioned the perils of airlocks, the difficulty of avoiding them and how they slow or stop the flow of water. This article is a bout a fix for airlocks - "vents"
If you've got some air trapped in a pipe blocking the water, you could knock a hole in the pipe to let it out but water would likely leak out too. The answer is to make sure the top of the vent hole is the highest part of the system. In the picture on the right, the main pipe is at the bottom while the vent is the vertical. The top of the vent is higher than the highest possible level of the rainwater butt. The 500mL bottle is just to keep dirt out.
A vent can be particularly useful near the bottom end of a system. Any air trapped there can easily escape rather than trying to fight its way all the way back up to the cistern.
A special case of venting appears below. A vent is connected to the far end of a special "leaky hose". Although such hoses are fairly porous, air can get trapped in them and such a vent helps a lot.
