Q&A / 

Sink P-Trap Substitutes

DEAR TIM: I saw a new device on a website that says it can replace the traditional p-trap under a plumbing fixture. It has a flexible tube-like membrane that is supposed to stay closed when no water is flowing down the pipe. I'm skeptical this thing would work over the long haul. I also wonder how things like this get approved by code officials? It seems the traditional p-trap under all my plumbing fixtures work well. What do you think about these mechanical plumbing products that attach to the waste and vent lines? Julie P., Rockford, IL

DEAR JULIE: Boy, oh boy, you sure know how to stir the pot! You also did a great job of touching a nerve I happen to have about plumbing devices and code officials. Let's open the discussion with the fact that I've been a master plumber for over 30 years.

I've got a new mechanical P-trap in my hand next to a traditional one that's worked flawlessly for well over 130 years.  Photo Credit: Tim Carter

I've got a new mechanical P-trap in my hand next to a traditional one that's worked flawlessly for well over 130 years. Photo Credit: Tim Carter

I'm pretty certain I've seen the exact plumbing waste valve you're talking about. When I first got it, I immediately recoiled at the design. My years and years of dealing with sludge-encrusted drain lines screamed at me this was a possible disaster waiting to happen.

Let's go quickly back in time to just after the American Civil War. If memory serves me right between then and the 1880's, the medical community came to a consensus about the connection between bacteria and diseases. Plumbing standards rapidly advanced and believe it or not, plumbers back then were often more highly regarded than physicians when it came to protecting the health of the general public. Plumbers were seen as knights in shining white armor.

That said, you absolutely never want to underestimate what can happen to you or your family if a plumbing drain system malfunctions or you have a polluted water supply system. Entire books have been devoted to the subjects.

Well over 100 years ago, it was quickly discovered you could completely stop vermin and bacteria from spreading into your home with a simple water seal under each plumbing fixture. They used to come in two styles: the S-trap and P-trap. They got the names because the shape of the drain pipes look like those letters in the English alphabet.

I have huge issues with mechanical plumbing drain and vent products that try to supplant the time-tested p-traps and traditional open vent lines that lead from fixtures up to the roof of your home. A mechanical device is one that has moving parts. We all know that every mechanical device known to man has failed at one time or another. If you know of one that's not, it will eventually fail.

You don't want a mechanical trap under a fixture that will not close off properly. When the trap remains open sewer gas or vermin can enter your home. What can cause a trap to stay open? If you've taken apart used p-traps and drain lines like I have, you'll quickly see biofilm, sludge, grease deposits, food chunks, gravel, etc. These can all interfere with a mechanical membrane that's supposed to close tightly.

Then there's the occasional vermin in the drain line. You do realize that rats routinely patrol municipal sewers and think nothing of making a foray up your house building drain and then into a branch drain line. How long do you think it would take a rat to chew through a thin flexible membrane only to stare you down at the sink stopper or basket strainer?

It gets worse in my opinion. I've never sat in on meetings where building code officials debate and discuss changes to the code. But suffice it to say that I've seen parts of the building code that make me shake my head. Some of the building code is not backed up with hard science, and/or the code officials have not seen as many old buildings I have that prove certain minimum standards must be always be adhered to.

You can't hope things are going to work. Hope is the emotion of last resort. You hope for something when you can't control the outcome. I can control the desired outcome in my plumbing system by using traditional p-traps and a real interconnected vent system that always supply air to the pipes as water rushes down them.

Realize the building code in your town is very possibly a hybrid of a national model code. The building and plumbing code can be different from state to state and city to city because local code officials can modify the model codes. I've also been told that some codes have provisions where a local inspector can approve an alternative material on his own. That's a very scary situation indeed.

Talk to any seasoned plumber and he'll tell you he's able to make a living because mechanical plumbing devices fail. Backflow preventer valves, regular valves of all types, pressure regulators, anything that has a moving part fails on a routine basis. Ask that same plumber about how well-designed and installed vent line systems work. I've never in my career had one fail. Never.

You can watch a pluming vent video and read past columns about p-traps showing how they work. Just type "vent pipe video" into the AsktheBuilder.com search engine.

Author's Note:

I received this very descriptive email from Ed Atterberry about an encounter he and his wife had with an accomplished swimming mammal. You'll see why P-traps are so important.

"Regarding the importance of traps on your plumbing, I offer the following true story. The date is sometime in the winter/spring of 1974. The location is Naha, Okinawa, where I was a teacher and my new bride was depressed about not getting hired and living in a foreign country where we didn't speak the language, etc.

Okinawa has a rainy season and a long period of dry weather. During the dry season, at least back then, the reservoirs would empty, and we would have to go on water rationing. The water would be shut off for certain periods of time. At this point, it was off at 10:00pm and came on at 6:00 am. It got much worse later on.

My wife woke up at around 5:30 am and had to use the bathroom. Since there was only one flush left in the tank, it was always a challenge to wait until you really, and I mean REALLY, had to go. (There was a workaround, but that involved filling the bathtub and then flushing with buckets of water, but that defeated the purpose of rationing water.) Anyway, she came back into the bedroom and asked if I had used the toilet and not flushed. Nope. But there was something dark in the bowl, and she didn't have her contacts in yet in order to see. So I haul myself out of bed and look in the toilet. Oops! A huge rat had invaded our toilet. Well, what to do? I brought the dog in hoping that she would scare the rat away. Not a chance. By the way, the rat did a passable breast stroke.

So I got a broom and hoped to bop it over the head with the broom handle. I didn't have a baseball bat handy. To be honest, I didn't have one in the house at all. I couldn't figure out how to get rid of the beast so my wife could use the toilet. Well, wonder of wonders, I soon heard the clattering of air rushing through the pipes, which was the forerunner of water that had been turned on. Within a few minutes, and about 20 minutes early, I could flush the toilet and say bye-bye to the vermin. He was nasty looking, believe me.

That's why it is so important to have traps that have water to seal off the pipes and keep the nasty critters out of your house. I'm still wondering how we would handle going to the base dispensary with a rat bite on her derriere.

And a corollary to that story. Years later, I was principal of a school in Chinhae, Korea. It was a small school with only two teachers and me. Of course, we were close friends with the entire staff. All two of them. One of them told a story that she had heard while working in Germany about a woman in Okinawa who went to the toilet and found a rat swimming around. Small world!"

Ed (KF6UQ)

Column 922

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