Open Thread - Saturday, December 17

Today's Open Thread will get a little practical: DWV basics.

What happens when you flush your toilet or run your washing machine or take a shower? If it's something bad, you have a problem with your Drain, Waste, Vent system. That something bad can be anything from a stopped up drain to a bad smell coming from your kitchen sink to a nasty leak down in your basement. Before you even call a plumber, you might want to know a little about how your DWV system is supposed to work, and even if you don't have a plumbing problem, maybe the day will come when you want to add a dishwasher or even an entire bathroom to your house.

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You may be surprised to learn that your home's DWV system is one of the more dangerous elements in your house. That's because sewage produces gases, including hydrogen sulfide, ammonia, methane, esters, carbon monoxide, sulfur dioxide and nitrogen oxides. Most of those substances stink, some are deadly, some are explosive. None of them are something you'd want in the air inside your house.

For a few months, we lived in a beautiful old stone inn in Istria with a view of both Motovun and Groznjan. It had a cesspool and a lousy DWV system. Things were so bad that we didn't need electric lights at night in the kitchen or bathrooms. We just lit the gas coming out of the drains, and that provided plenty of illumination. Just a little hyperbole, but it did stink worse and worse, and if we had let a bathroom door remained closed and unventilated for a period of time, who knows what would have happened if there had been a spark or flame?

How does a proper DWV system prevent that sewer smell? It combines a system of traps to keep the nasty gases out of your home with a system of vents to take the sewer gas outside where it can dissipate more or less harmlessly into the atmosphere.

Where are the traps? Look under your kitchen sink. You should see something like this:

kitchentrap.jpeg

See the larger, white pipes? That's part of your DWV system. It's made of PVC plastic in the picture but can be made of metal or other plastics. Note the U-shaped section of pipe. That's where nasty stuff often likes to collect, sometimes to the point that it stops up your drain partially or even completely. But the installing plumber didn't put that U-shaped section there to be a nuisance and a source of future income. That section is the trap for a double-bowl sink, and it's there to hold water at all times so that the nasty sewer gas on the other side of the trap doesn't come up through the drain into your kitchen.

You'll also note in the picture how that white pipe has what looks like spoked wheels at several points. Those are connectors that can be screwed and unscrewed by hand so that you can remove that trap and clean it physically if it gets blocked. If you ever decide to DYI a stopped-up drain without using Drano, be sure you keep that U-shaped section in its original upright position until you empty it in another plumbing fixture or you'll have some dirty water all over yourself and your kitchen cabinet.

These traps are present wherever you have a plumbing fixture. For your washing machine, it might be in the wall just below the standpipe where your machine empties. Your toilets have a trap built in--with some toilet designs, you can see that U-shape at the base of the toilet. Your lavatories have one. So does your shower. Even though they have a natural tendency to collect hair and food scraps and whatever to the point of getting blocked, they are what make modern plumbing work.

So far, so good, but you report that your kitchen sink still gets that sewer smell from time to time even though it has a nice trap like the one in the picture. The problem is that there's something about your DWV system that is causing the water that's supposed to always be present in the trap to get sucked out and pulled down the drain, leaving your house exposed to the sewer monsters.

The two main causes of water getting sucked out of traps are siphonage and back pressure. Siphonage takes place in one of two ways. First, the fixture in question may send water down the pipe so fast and in such quantities that the air is sucked out of the pipe beyond the trap and air pressure pushes the water out of the trap and down into the sewer. Second, a fixture above may send waste water down the main stack so fast and in such a quantity that it sucks the air out and the trap water is lost. Back pressure results when sewer gases build up beyond the trap to such a point that they push the trap water up and out of the drain.

All of these problems can be prevented by proper venting. Any general plumbing book and this nice web page will include a table of DWV pipe sizes and the maximum distance of a run before a vent is required. If your kitchen sink smells from time to time, chances are that it's not properly vented. The stop-gap solution is to gently refill the trap with water from your kitchen faucet when it smells. A longer term solution that doesn't require ripping out any walls would be to add one of these nifty little vents between your trap and where the pipe goes into the wall. These vents work for smaller drains by only allowing air in and not out.

Back pressure can be prevented by making sure the gas in the system has an exit. If you check the roof of your house, you'll probably find one or more DWV vents. Just like gas fixtures like furnaces or hot water heaters need a vent to remove nasty waste gases, your DWV system needs one or more vents to the outside. Usually, these go through the roof at the top of a "stack." That's how things are designed in the first drawing above in which that house has three stacks, the long, vertical pipe sections to which several plumbing fixtures are attached. Each of these stacks continue past the uppermost fixture up and through the roof. That's where the sewer gases exit. It's also where air enters that is needed to balance air pressure and keep water from being pulled from the traps. if some odor-indifferent birds or wasps decide to build a nest in your DWV vent, then you have a problem that will take a ladder, decent balance and maybe a little courage to fix.

That's the basics of a DWV system. There are lots of other issues to consider. Pipe slope is critical. If it's it's not "downhlll" to the sewer, waste water will back up. If it's too steep, the water will flow too fast and leave solids behind, a very bad thing in the long run. DWV systems must be airtight to prevent gases from escaping into your walls or basement. That's why a plumbing inspector requires a pressure test before approving an installation. Plumbing codes covering DWV systems are lengthy and technical, but a fundamental understanding of how a DWV system works will help you deal more effectively with plumbers if you're calling in help or will keep you from making potentially dangerous mistakes if you're a DYI-er.

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We're putting in another section of DWV pipe for the fourth and final bathroom in our house. I promise not to inhale too much glue so I can come back here and respond to comments.

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riverlover's picture

And my 34 y/o double kitchen sink I think has had the trap replaced once, and if there is a dishwasher attached to that as well, you really don't want that trap to fail. A messy flood may happen. I also have a new fridge with an icemaker in the freezer, but I never plumbed to that, and will not. Rumors and stories of leaks in the fridge water supply line are everywhere. I should remove the icemaker and free up 20% more space in the freezer.

Coincidentally, got a call from daughter at 8AM today that her house was at 58 then 57 degrees. It's in the teens outside. Her furnace is gas, and it's running, obviously no flame (my guess, educated). Another Saturday emergency. They have lived there for over a year and no one has even replaced the filter. So 2 clueless people. Thank FSM I lived with an architect for 32 years and learned a lot by osmosis.

Goin South, are you using PEX for supply lines now? I have a 4'run of PEX to a toilet that was forever filling slowly since installation, my husband did the copper piping to it and over-soldered one or more joints that filled the pipes with solder. So a hole in the drywall and PEX and than a drywall finisher to fill in the hole later, I am done, except that toilet is at grade on slab and is early low-volume flush and tends to clog with, um, stuff that should go in a toilet. After the first and last plumber call for that, I have been advised that better toilet designs are on the market and if it happens again, toss the toilet.

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Hey! my dear friends or soon-to-be's, JtC could use the donations to keep this site functioning for those of us who can still see the life preserver or flotsam in the water.

When we do a bathroom in the now-vacant "little house," I may try PEX since I'll be starting from scratch there.

I do think those low-volume flush toilets are getting better and better. It might be worth replacing it if you're having trouble.

We're having a thaw here in Cleveland today. Should be getting to you before long.

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riverlover's picture

I had my entire cottage that had plastic tubing for supply lines because it had no heating source in the cold Canadian winter. Every year at cottage close, we had to blow air through the lines to remove water, fill all traps with antifreeze, drain the water heater and toilet, etc. Face-to-face with plumbing. We had a plumber re-connect the system to the well and check every spring for leaks. One year, he missed one, the old hot water heater (power off) blew out the bottom and because power was on at the pump, filled the lower floor with water. Insurance claim. Ruined furniture. I re-plumbed with PEX (and not me) also upgraded wiring and started a complete re-do. I am now suing the contractor for fraud. $100K lost into the St Lawrence River.

I sold the place a week ago, not my away headache any more. Wink

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Hey! my dear friends or soon-to-be's, JtC could use the donations to keep this site functioning for those of us who can still see the life preserver or flotsam in the water.

travelerxxx's picture

Interesting essay, GS. Just yesterday, I was considering what it takes in a town or city to get all the sewer pipes to work correctly. In other words, "...Pipe slope is critical," as you mention. The engineering required to make our waste water head in the correct direction is something not often pondered, but - as you have experienced - it's critical.

Evidently, there is "system low-point," which must surely be the local waste treatment plant (or septic system if you're not part of a public sewer system). Everything else has to be on an upstream slope from that point. So, from the waste treatment plant all the way to one's kitchen sink, the entire system had to be considered. How this is all laid out, measured, built, and maintained is a bit of a wonderment to me.

Recently, I saw a meme photo showing a row of snowplow trucks clearing a snowy roadway. The caption simply stated "Socialist Snowplows." It occurs to me that our Libertarian friends, should they be true to their beliefs, should take themselves off our "Socialist Waste Water System."

There's much we take for granted - and if you've got wastewater problems, you won't take that system for granted for long.

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melvin's picture

A very good friend just died. We have talked for many years since our expulsions from guess where, through many sorrows and joys. A mutual friend just contacted me this morning; otherwise it might have taken quite some time for me to figure it out.

It seems right to leave it up to her sister to announce on her timeline. But beyond that, is there a protocol? There are people who would want to know. Mention it on my fb? And of all things I am very concerned about her dog, currently shunted off to the Humane Society in San Jose. We are looking into somehow sponsoring an adoption. (If you are near there, she is a beautiful miniature pinscher.)

The more ancient among you may remember her as "dwijas" on dkos, and later as "boriskamite". Possibly a few other pseudonyms I didn't know about.

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enhydra lutris's picture

thing to have. Also, some p-traps have a built in drain/clean-out on the bottom, which is useful.

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That, in its essence, is fascism--ownership of government by an individual, by a group, or by any other controlling private power. -- Franklin D. Roosevelt --

Lookout's picture

sure has made plumbing easier. I remember (back in the dark ages) running cast iron sewer pipe and galvanized supply lines.

I used pvc when I built 30 years ago. When I came back and added radiant floor heat, I used PEX. We also have a gutter and cistern system (2000 gallons) which involved a little plumbing. I spent a summer when I was 18 as a plumber's helper. One of the most educational jobs I ever had.

Good luck with your project, GS.

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“Until justice rolls down like water and righteousness like a mighty stream.”

mimi's picture

find here. I have lots of respect for good plumbers and electricians and wished I had the nerves to try to do it myself more often. May be one day I get that "little house" that needs fixing. Sigh.

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magiamma's picture

This was posted on JPR. The link below is to the sourced article.

On the morning of Dec 16,2016, NATO officers were arrested by the Syrian Special Forces in a bunker in East Aleppo:

http://www.globalresearch.ca/breaking-fourteen-us-led-coalition-military...

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