plumbing

We all know that the waste water from a sink, a sink, bathtub or toilet pass through pipes hidden under these various devices and flow into underground sewers and eventually end up in municipal sewers . Most plumbing is hidden in the walls and it can be difficult to imagine that there are vertical drains, which go to the top of the roof. The outer parts are called "vent".
Although the water in these pipes are as tiny droplets of steam without the presence of these vents, the sewage would be impossible. It is thanks to gravity and unevenness that liquids can flow.
However down the amount of fluid that pushes the air in its path and creates a vacuum behind it. This negative pressure increases to be equal to the force of gravity. It was at that time that the water movement stops.
However, if air was introduced into the pipes, the vacuum could not exist. This is the reason for the existence of vents that are unnecessary air escape into the atmosphere. There is another reason for the need to expel the air in the atmosphere: the decomposition of organic waste into municipal sewers can create an issue of methane gas that can repress. Vents expel them easily.
So you can see for yourself the effects of negative pressure created by water falling colliding in the air and in turn creating a vacuum, I suggest you do the following test:Fill your sink to half fill a bottle almost a pint brim, then did the same with a bottle of plastic two-liter (soda for example). No need to be a whiz in math you realize that the second bottle is four times the volume of the first and is therefore heavier.
Reverse the 2-liter bottle by immersing it in the sink with the opening of the bottle under water. You will find that the combined weight to the weight of preventing water from escaping. In fact, a vacuum (like a hood!) Formed in the tip of the bottle and the vacuum prevents water from escaping and the force of gravity alone is not enough. Lift the bottle just above the water level and you will see that the amount of liquid that will flow from the bottle will be equivalent to a small amount of air as bubbles will enter at the same time, to take instead of water.
The next time you renovate your bathroom or add one in your basement, call a plumber who understands the relationship between drains and vents.