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What Happens If You Pour Water down a Vent pipe?

What Happens If You Pour Water down a Vent pipe?

We all have vent pipes on the roof & some of them are straight. So whenever it starts raining, water goes down the vent pipe. Also, people have to clean the pipe so they start thinking what happens if I pour water down the Vent pipe?

I have done some experiments on this & today I will explain all the results I got for you.

If you pour water down your vent, it will not affect anything instead it will go down to your drain because the vents are connected to the main sewer line just like your kitchen sink water or your toilet. And even If you pour hot boiled water down, it will not affect anything on your vent.

Why is vent pipe important?

Before you flush a toilet or let the war go out of the sink inside the sewer & drain line is nothing but air. As soon as you pull the flush of the toilet, an enormous amount of water pushes down through the pipe and pushes the air out of the way.


That air needs to be replaced and it does it through the vent lines as the water travels down towards the sewer or your septic tank air enters through the roof and comes down into the line to replace the air that was pushed out of the way.

Have you ever noticed, when you flush a toilet? You hear a gurgling in your bathroom sink or maybe your bathtub. It’s a sign that the event line is clogged.

How to fix it?

Get up on the roof, put a garden hose down the stubby pipe & turn it on. Make sure someone is inside to check for leaks.

Can I pour boiling water down a PVC pipe?

It depends on the hotness of the water.

PVC pipe was built in a way that it can resist hot water but it has a limit. Normal limits are 120F / 50C for regular PVC (not CPVC).

If you pour too much hot water down any PVC pipe, the inside will start to warm up but the outside of the pipe will still be cold and stiff.

It gets pretty droopy at 140F / 60C. Code does not allow any liquid/wasteto go into the system over 140 degrees Fahrenheit. It doesn’t even matter the composition of the piping, ABS, PCV, cast iron, or DVW copper are all included

If you have any bend shape in your pipeline, the hot water will probably stuck there & it may make the inside part of your pipe warm up.

People have a pot of pasta water all the time, dump it into a strainer, and right down the drain of the kitchen sink. Yet no one ever complains about any problem.

Part of it is that the water cools 10–15F just from pouring it, it flows over the cool sink basin and the pipe started at room temperature. And the pipes, hopefully, aren’t under strain – when I’ve had hot PVC creep on me, it was being under tension, torque, or containing pressure.

Can I run water down my drain vent to clear it?

From a technical plumbing POV, the answer is yes, but something unexpected can happen. You need to be sure that the pipe is fine & connected to the drain pipe properly.

For example, if your vent pipe is clogged, the water that you will pour into the vent pipe will not go down the drain. The situation can go even worse if there is any scratch on the vent pipe.

Does rain water get into a vent pipe?

Of course, if it’s plumbed like this. But if your pipe is fie it’s not a problem.

Should vent pipes be covered?

Vent pipes should be open to the atmosphere (plumbing). Other types of vents may be covered in some fashion but that will not interfere with their ability to ventilate and may require a flap to exclude vermin or other special features.

Never cover a gas vent. Never cover a plumbing vent. Avoid using so-called “Chinamen’s caps”.

What is the best way to clear a residential vent stack pipe?

Plumbing stack – I just use a drain auger, the same type I use to clear clogged sink or tub drains. On occasion, I have cleared clogged drains on upper-level units by going down the vent pipe as well. As others have suggested a garden hose will work well too. Some caution is advised if you turn on the water. Make sure it is not coming out through the fixtures below.


A vent pipe is important to maintain the good functionality of your plumbing system. So keep it in good condition. If anything goes wrong, call an expert.

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