We’re going to get a little technical this week, but break it down in a way we can all understand. We’re going to talk about what we plumbers call the DWV (Drain, Waste, and Vent) System. This is the piping system that if done correctly, allows everything to flow smoothly away from your toilets, sinks, etc., and into the city sewers.
A DWV system essentially has piping classified into two sections: drains and vents (there is a difference between “drain” and “waste” pipes, but its not important for today).
Drains are heavily reliant on vents in order to work properly. The purpose of a vent is to replace the displaced air “behind” the flowing water. You may be thinking, why is this important? Well hold onto your hats and let me tell you!
I like to use the analogy of an old apple juice tin: Remember when you would make just one hole in the top and pour the apple juice into your cup, how it would glug, glug very slowly? That’s the same idea as what is happening when there is a drain without a vent. Now, think of what happened when you made that second hole on the other side of the apple juice tin – all the apple juice you could drink! That second hole is the vent.
The reason the apple juice glugged out when there is only one hole, is because the apple juice was fighting to come out, while air from outside was fighting to come in to fill the space that the apple juice created. If you picture what is happening inside the tin, the space that the apple juice once filled has to be replaced with something, and that something in this case is air. With only one hole, the apple juice and the air had to take turns – glug, glug, glug. Introducing that second hole and all of a sudden, the apple juice flows freely. It’s no longer fighting against the air – happy breakfast time!
It is not so much of an issue in larger buildings like apartments, condos, or townhouses, but in older homes we seem to have a lot of trouble with this system. Over the years, DIYers and unknowing contractors will have often cut out these vent pipes that they see as unnecessary. As you can guess, that is a bad idea!
When you have slow flowing drains as a result of a venting issue, you are much more susceptible to blockages, buildups, etc. This is why we don’t play around with things when we don’t know exactly what we’re doing! Getting rid of that small bulkhead in your bathroom may seem like a great idea at the time, but you won’t be happy calling me every few years to run my snakes down the drain.
That’s it for this week! I hope we were able to break things down a little bit so that you could all have a basic understanding of the piping system. It can seem quite complicated (and it can be), but in many cases it is quite a basic system!