Bathtub drain plumbing does a lot more than allow your bathtub to drain the water at the end of your bath.
In fact, there is a lot more going on down there than you might expect. If you don’t believe me, take a look at the pipes under your bathroom sink.
Why does the water go to a “U” shaped pipe instead of dropping straight down to the sewer drain?
What does any of this have to do with your bathtub drain plumbing?
The reason why drains don’t go straight down to the sewer is that while it would be more efficient and eliminate clogged pipes, it would also allow dangerous sewer gasses to seep into your home.
Sewer gasses are composed of a number of different gasses including hydrogen sulfide, ammonia, methane, carbon dioxide, sulfur dioxide and nitrogen oxides, which can be toxic, flammable or both.
If you aren’t a plumber or familiar with local building codes, you may not have realized that there is a system of air venting pipes that run from your roof to all of the drainage pipes in your home.
Water runs out your bathtub drain plumbing when you pull the plug because water is replacing the air in the pipes. The noise that you hear when the bathtub is nearly done draining is the water making a vacuum in the “U” pipe, which prevents the sewer gasses (or small animals) from proceeding up the pipes.
Proper plumbing has a lot to do with the health and welfare of you and your family. Please make sure that you know and understand your local building code or hire a trained and professional plumber before attempting any repair.