Science (Plumbing) Problem

[street]

I agree. But we only see the drain line until enters the wall. Maybe it runs horizontally or even slightly uphill for several feet before going down?

This could be the problem I agree.

 

[ERD50]

Quote:
Originally Posted by Music Lover View Post
I agree. But we only see the drain line until enters the wall. Maybe it runs horizontally or even slightly uphill for several feet before going down?

This could be the problem I agree.

Yes, could be (I had to think twice about it).

If the drain pipe rises up close to the height of the bottom of the basin, then there is very little pressure difference between the two, and water will flow slowly. But a full basin will have a larger difference, so more pressure difference ( ~ 0.5 PSI per foot of vertical height).

edit/add: This was discussed in post #53, and NW-Bound made a suggestion on how to determine if this is the cause, w/o opening the wall (water level will be above the trap - remove the AAV to check this).
-ERD50

 

[mountainsoft]

Note that even if the vent in your house was blocked, the drains would still be open to the atmosphere through all your neighbor's houses and their vents.

Unless you're on a private septic system like us.

When we built our house I wanted to minimize roof penetrations so all of our fixture vents tie into our single 3" vent that exits the roof. I have a cap on the vent to prevent birds or other debris from getting into the vent pipe.

 

[ERD50]

Unless you're on a private septic system like us.

When we built our house I wanted to minimize roof penetrations so all of our fixture vents tie into our single 3" vent that exits the roof. I have a cap on the vent to prevent birds or other debris from getting into the vent pipe.

Nope, even a private septic will have the drains open to the atmosphere, even with the roof vent blocked. I mentioned this earlier, as our previous home was on septic.

The cover on the septic tank is not air-tight. And the ground will be permeable enough that over the entire drain field, air can be exchanged with the atmosphere. That cover is tight enough that you don't get so much leakage that you get odors, and there is a fair amount of air volume in the septic tank and drain field, so pressure will equalize with the atmosphere, even if your roof vent was blocked. The headspace volume "cushions" any sudden rush of water entering the system (a toilet flush).

Now, if the roof vent was blocked, you'd get vapors leaking around that cover or any other path through the drain field. The 'fermenting' 'stuff' creates expanding gas. If it can't get out through your roof vent, it will find its way out through the cover or field.

Also, I'm curious as to why it isn't common to run the vent stack out the side of the house, then up over the the roof (there's some code on how high it has to be). That would eliminate a roof penetration and chance of a leak. Might be unsightly, and would need some support, so maybe that's why it's not done?

-ERD50

 

[Gumby]

...

Also, I'm curious as to why it isn't common to run the vent stack out the side of the house, then up over the the roof (there's some code on how high it has to be). That would eliminate a roof penetration and chance of a leak. Might be unsightly, and would need some support, so maybe that's why it's not done?

-ERD50

Around here, where there are still houses from the 17th, 18th and 19th centuries that originally were built without indoor plumbing, you will occasionally see the main drain pipe running up the outside of the house, with a top-hat vent above the roofline. The bathrooms on each floor and kitchen are usually stacked one above the other, with a horizontal connection through the exterior wall to the drain. Because that's the only way they could back-fit plumbing into the house.

 

[Music Lover]

Also, I'm curious as to why it isn't common to run the vent stack out the side of the house, then up over the the roof (there's some code on how high it has to be). That would eliminate a roof penetration and chance of a leak. Might be unsightly, and would need some support, so maybe that's why it's not done?

-ERD50

I would find that unsightly. Theoretically, it's not difficult to properly seal a vent stack in the attic and through the roof. In the real world though, sometimes it's not done correctly.

 

[Telly]

....Again, the vent stack is to prevent the "slug" of water coming out of one fixture from sucking water out of other traps. Nothing else. -ERD50

If one removes the vent pipe from the top picture, so the drain pipe is continuous from sink to down out of the picture, then the difference between the top pic, and the bottom pic, is slight. With that modification to the top pic, it becomes a self-starting siphon when the volume of water descending the pipe, fills the pipe.


A simple experiment to show this, that anyone can try: A length of clear flexible vinyl tubing; a funnel whose neck fits tightly into the tubing; a bucket; a sink with running water


Instead of going to bed after reading this thread last night like I should have, I hunted up the tubing and found a funnel that fit well. The setup: Funnel is held under a faucet, with the tubing going down into the sink a ways, then it travels up and over the sinktop edge, then down to a bucket. I lightly pinched the tubing with my knee against the cabinet (only enough to hold it in place, not enough to deform the tubing, which was pretty heavy-wall anyway). I adjusted the tubing so it made a "trap" down below the funnel, I on purpose did NOT make a long deep trap, as I wanted to approximate a real-world P-Trap. My knee pressure held the length of tubing, so the P-Trap depth stayed constant.


I started slowly filling the funnel with water, filling at an edge, as I wanted any air put in the water by the faucet's aerator to not go straight down the neck of the funnel. Looking at the tubing, could see small slugs of water interspersed with air slugs. If I turned OFF the faucet, no syphon action occurred, as the stream of water in the tubing was not filling 100% of the tubing's volume.


I turned the water back ON, filling it faster. The slugs of air disappeared, the tubing's volume was now all water. I then turned the faucet OFF. The water was zooming down the tubing, and then the funnel made sucking sounds for a moment. The siphon effect had sucked the water out of the tubing, and out of the "trap". There were still water droplets and a film of water in the "trap". In a moment or two, the water bits, due to gravity, collected in the bottom of the "trap". It was just a small bit of water that collected, about 1" long in the tubing's "trap". Very little water, as compared to what the "trap" could hold. So in the real world, that small amount of residual water left in the "trap" could evaporate, allowing sewer gases to rise from sewer into house.
Thusly, the vent line in the top picture is important to the trap in the pic.


It's an easy experiment to implement

 

[travelover]

.....It's an easy experiment to implement

I wonder if this would work to steal gas out of a parked car?

 

[Telly]

I wonder if this would work to steal gas out of a parked car?

Sinks, toilets, tubs and showers don't have rollover check valves in them

 

[JoeWras]

Oh man, living in a large urban area in the 70s... Gas siphoning was a crazy real problem! Hence the anti-siphon devices that got added.

 

[ERD50]

If one removes the vent pipe from the top picture, so the drain pipe is continuous from sink to down out of the picture, then the difference between the top pic, and the bottom pic, is slight. ...

NO!!! There is still an *important* difference between the two. Having the 'trap' rise above the level of the liquid in the sink creates a very different situation. The trap above the level is a siphon that must be started with an external force to counter the force of gravity. The trap below the level of the sink just fills because liquid will seek its own level, gravity assures it.

.... I started slowly filling the funnel with water, filling at an edge, as I wanted any air put in the water by the faucet's aerator to not go straight down the neck of the funnel. Looking at the tubing, could see small slugs of water interspersed with air slugs. If I turned OFF the faucet, no syphon action occurred, as the stream of water in the tubing was not filling 100% of the tubing's volume.


I turned the water back ON, filling it faster. The slugs of air disappeared, the tubing's volume was now all water. I then turned the faucet OFF. The water was zooming down the tubing, and then the funnel made sucking sounds for a moment. The siphon effect had sucked the water out of the tubing, and out of the "trap". ....


It's an easy experiment to implement

This might not replicate the sink issue exactly. In a sink, you have a 1 1/2" drain pipe. Unless you stop up the drain and let a large volume of water accumulate in the sink, I doubt that you fill the drain with water. It normally would just flow up/over the horizontal section. Also, your small diameter tubing is affected more by surface tension, trapping air bubbles because of it.

But close enough. If you did the "full basin-fast drain" thing, and if that filled the pipe with water, the flow down the drain might be powerful enough to suck the water out of the trap. But more likely, as the flow slows as the basin empties, the drain pipe won't be full, it turns to a trickle, and air will seep back in (the drain is open to the atmosphere at some point) and the trap will fill.

-ERD50

 

[ERD50]

OP here. I really appreciate all responses. ....

I'm tend to be slow and deliberate so I don't have a time table yet, but I will definitely let you all know how this story ends. Thanks for all the help.

OP, any update? It's been over a week.


-ERD50

 

[Mark1]

OP here. Enclosed is how the story ends.

With a flashlight looking down through the strainer it became quite obvious that air was indeed covering the bottom of the strainer and blocking the path for water to leave the sink. However, there was no way I was drilling out the strainer (or installing a new open tail piece piping) and permanently seeing all the soap scum on the piping inner wall, so I started looking around for something to cover the strainer area and hide the view. I ended up finding a “sink basin trim overflow brass insert” on Amazon so I ordered it to take a better look at it (see photo below). The style and finish matched my faucet, so I ordered a 13/16” drill bit and installed it within the sink strainer as shown in the photo. It works like a champ. Due to the small cross section area of the insert, I can build a water level if I leave the water running for an extended period of time, but it always drains within a few seconds. Problem solved.

I also removed the aerator while installing the insert and I put the piping back to the original design. Other than the these actions, I haven't performed any of the other great ideas and suggestions I received from folks. I'm just so busy being fired.

Thanks again to all. I appreciate the help and I did learn a lot.

 

[ERD50]

OP here. Enclosed is how the story ends. ....

Problem solved.

I also removed the aerator while installing the insert and I put the piping back to the original design. Other than the these actions, I haven't performed any of the other great ideas and suggestions I received from folks. I'm just so busy being fired.

Thanks again to all. I appreciate the help and I did learn a lot.

Thanks for the update, glad it all worked out.

And just in case that Air Admittance valve was needed for anything (a blockage in the vent?), listen for any gurgling sounds in the trap when other sinks/toilets/etc are being used. That AAV would keep the trap from being sucked dry and letting gasses into the room.

I have a few seldom used drains, I try to remember to pour some water in them once a month, as the water in the trap can evaporate.

-ERD50

 

[6miths]

Yes thanks for letting us know. Glad you got it fixed.

 

[NW-Bound]

OP here. Enclosed is how the story ends.

With a flashlight looking down through the strainer it became quite obvious that air was indeed covering the bottom of the strainer and blocking the path for water to leave the sink...

Glad to hear that you found air trapped under the strainer being the cause of the problem.


.

 

[JoeWras]

Glad to hear that you found air trapped under the strainer being the cause of the problem.

.

I really find this issue fascinating! Makes sense. It is something I've never encountered since all our sinks are mushroom-pop-ups. The kitchen sink is an exception, but that strainer has a lot of surface area.

Thanks for the update, OP. I need to add it to my list of possible plumbing problems.

 

[ERD50]

I really find this issue fascinating! Makes sense. It is something I've never encountered since all our sinks are mushroom-pop-ups. The kitchen sink is an exception, but that strainer has a lot of surface area.

Thanks for the update, OP. I need to add it to my list of possible plumbing problems.

But I have noticed that if the "mushroom" isn't open far (maybe only 1/8", 3/16"?), that air can get trapped, I'll see a bubble, and the flow is slow (heck, I guess we could do some poetry in any thread! ). I never paid too much attention, would open it further if I really did want it to drain faster, or just tap it to break up the air bubble.

And I suppose a full sink would have pushed that bubble out, but I never noticed.

-ERD50

 

[NW-Bound]

I really find this issue fascinating! Makes sense. It is something I've never encountered since all our sinks are mushroom-pop-ups. The kitchen sink is an exception, but that strainer has a lot of surface area.

Thanks for the update, OP. I need to add it to my list of possible plumbing problems.

It's the perforated strainer that gives the OP the problem. Look again at the photo at the top of the thread, you will see that the holes are all at the same level. With a thin layer of water on top, all the holes are under the same depth of water, and this equalized pressure means the air cannot bubble up.

Additionally, usual bathroom sinks have an overflow channel. Most people do not notice it because the overflow hole in the sink cannot be seen from the front. Lean forward towards the wall, bend your head down and look back towards your tummy. You will see the overflow outlet there at the front side of the sink. Air can escape through there, even if the drain plug is not of the popup type.


For the kitchen sink, two different things exist.

First, most kitchen sinks are dual, and the two sinks usually are connected together above a common J trap. Air can escape from under the sink being drained, out through the other sink.

Secondly, the kitchen sink strainer has radial slits, and the shape of the strainer means that the slits are not all at the same depth of water. The outer ends of the slits are under shallower water than the ends at the center of the drain. Air will bubble up at the shallower spots.

 

[mountainsoft]

I have a few seldom used drains, I try to remember to pour some water in them once a month, as the water in the trap can evaporate.

I have to do that with our guest bathtub. Since our daughter moved out it never gets used. With no one using it we rarely even need to clean that tub. So I try to run the faucet there every now and then to refill the trap.

 

[Gumby]

About the danger of a dried out trap.

We have a downstairs shower that we never use (it is a dandy spot in which to keep the cat box). About 15 years ago, when it was new, the trap dried out. As I was searching high and low for the dead mouse I was sure was causing that odor, I used my wheeled swivel/tilt office chair as a step stool and - you guessed it -- fell right off and broke my arm. The young wife came in the office and saw me writhing on the floor in pain. "What happened?" she asked. "I fell off the chair," I explained. "Well, that was stupid," she observed as she walked back out.

So now, I periodically fill the trap with water, so that a) I don't hurt myself and b) I don't get dunked on by the young wife. And also so it doesn't smell bad.

 

[Winemaker]

In those seldom used drains, pour some liquid detergent in. The detergent will float on top and not evaporate as fast as the water. Pine oil used to work better in old timey days.

 

[JoeWras]

If building new, and you have a basement floor drain, try to get a trap primer installed on the floor drain. This needs to be designed and roughed in. It usually is not an easy retrofit.

It works by throwing an ounce or two at the drain on every toilet flush. This is done through a small unobtrusive pipe.