IS YOUR KITCHEN SINK NOT DRAINING, BUT NOT CLOGGED?
“My kitchen sink has not been draining properly for months. When running the tap, the sink will fill up and drain very slowly. We’ve put commercial drain cleaners down it (including an enzyme based one, which we were told is what you use if there is no actual blockage?), but they’ve done no good. Also tried a bucketload of caustic soda, which hasn’t solved the problem either. We were told that it could be a venting problem.”
A vent stack is the pipe (usually inside a wall) that goes right up through the roof. it allows vapors to escape the house. It also allows pressure equalization. That is to say, if you didn’t have this stack the drains will not work very well.
If it is the vent stack, and it is plugged, when you get it open it will allow air to equalize in the sink drain. This is very similar to your ears popping when you go up in a plane. The pressure outside your ears is lower than inside your ears so the ear drum “pops” from pressure. If you swallow hard you “equalize” the pressure. Well this is similar to the vent stack’s function. If the stack allows air out (and in at times) it then vents the sink so that when the sink drains it doesn’t need to “burp” or “build pressure to a head”.